There are times when having a large law firm work on a case can be an advantage.
It is rare for the number of lawyers working on a particular case to be more than three or four plus a few paralegals, even in a case where there are virtually unlimited resources at a party's disposal.
In those cases, the primary benefit of having a large law firm at your disposal is that by paying top dollar for those attorneys, you may (but certainly don't always) get particularly competent attorneys at firms that have good systems in place.
If you are willing to spend the money you can also have the attorney and paralegal team work exhaustively to leave no stone unturned in terms of legal research, style and proofreading, "wild goose chase" factual and legal research of matters like trial court arguments from other cases that the opposing counsel has participated in, and trial presentations with lavish presentation quality.
For example, in one case where my firm was litigating against a large law firm in state supreme court arguments, the firm had seven law firm partners who had served as clerks in that court earlier in their careers participate in mock oral arguments to help the appellate lawyer who would be presented the case in oral arguments to the Colorado Supreme Court prepare (with four members of your core team and seven mock justices plus some paralegals participating this was a $5000+ per hour activity).
A typical run of the mill appellate brief prepared competently might take 100 hours, while a large firm might devote 800 hours to the same task (both of these are hypothetical round numbers suggested just to get the point across).
This incredibly intense working up of cases, moreover, often involves attorneys who aren't really starting from scratch as they has handled many similar cases before in their careers, while their smaller firm competition may have only encountered the issues presented for the first time.
You are also paying for connections and experience. For example, a large law firm may have an easier time retaining the most decorated expert witnesses to argue on their behalf. These attorneys may also have handled numerous cases in front of the judge or judges who will be deciding the case (and if they haven't someone else in the large firm probably has) and thus can better predict what approach will be received best by that particular judge.
The exception to the rule that the maximal economies of scale are reached with a quite small group of lawyers is that in addition to this core group of lawyers, some cases, such as class action lawsuits, or cases involving complex transactions (e.g. construction project disputes in a large project with hundreds of contractors) may require an immense amount of factual discovery in the trial court in the form of depositions of dozens or hundreds of people with relevant knowledge, and/or review of vast volumes of documents (e.g. I've had several cases with whole rooms stacked floor to ceiling with relevant documents in banker's boxes).
In cases like those, you need an army of senior paralegals and junior attorneys to interview witnesses, take depositions and review and summarize documents to get to the bottom of the factual matters needed to prove a case.
The down side of this approach, however, is that it is extremely expensive relative to the alternatives per task, and frequently impossible to recover your costs and attorney fees from the other party, perhaps because they aren't permitted to be awarded, perhaps because a judge would find some or all of your fees and costs to be unreasonable, or perhaps because the other side simply can't afford to pay them.
So, using a firm like this really only makes sense if the stakes involved are very high, or if there are long term strategic reasons to litigate. Spending $1,000,000 on attorneys' fees and costs is a very expensive way to litigate a $100,000 one off dispute. But spending $1,000,000 on attorneys' fees and costs is perfectly sensible if there is $100,000,000 in controversy in the case at hand, or if a favorable outcome will influence the outcome of a large number of future disputed of the same type.
The other dirty little secret is that lots of the work done by large law firms for which their clients pay an immense amount of money isn't done very well. One inherent down side of being large is that a large law firm is bureaucratic and prone to the kinds of mistakes that all large organizations have, for example, in diffusing responsibility for mistakes that can allow mistakes to fall through the cracks. Also, while the typical large law firm lawyer is typically more knowledgable than the typical small firm lawyer about the field at issue, this doesn't always happen. Sometimes junior attorneys get assigned too much responsibility on cases in areas where they have blind spots in their knowledge, and sometimes a large firm attorney ends up working a case due to personal connections with the client rather than because that attorney is the most qualified person in the firm to handle it.
Also, while some very brilliant lawyers do indeed work at large law firms, technical competence isn' the only consideration in hiring. Successful large firm lawyers need to be team players, need to conform and function well in a large bureaucracy, and need to have the social capital to be comfortable on a day to day basis with the firm's other lawyers and their affluent and big business clients. Many large firm lawyers have those soft skills while having only competent rather than excellent legal acumen.
Further, since most large law firm lawyers go straight from law school to a big firm (sometimes with a detour clerking for a judge for a couple of years), and large law firms handle mostly very big cases that are usually settled by lead attorneys before going to trial, most large law firm attorneys aren't particularly experienced at trial work. Some large law firms compensate for that by laterally hiring former prosecutors, former criminal defense lawyers and former high volume personal injury litigators to do that work, but often, large law firms have few lawyers in the courtroom with much trial experience relative to how many years they have practiced law. They may be very well prepared, but often there is no substitute for hands on trial experience.
Still large law firms tend to fight extremely hard in trial, but tend to be pushovers in settlement discussions. This is driven by the reality that the client will incur huge amounts of attorneys fees and costs to go the distance, and by the fact that professionally, the worst thing that a large firm lawyer can do it to have an unexpected and unpredictable bad outcome at trial. So, large firm attorneys seek to give their clients low expectations about what is possible in litigation in order to make it possible to make cases with significant uncertainty go away with settlements larger than would really have been necessary to settle the case with a more total client litigation and settlement cost sensitive law firm.
