The primary ideology in legal writing is "use what has worked". This is a millenium-old practice in the common law tradition (predating the development of what is known as "the common law"). This explains the substantial similarity between legal documents, and is responsible for the rise of "legalese" – legal writers do not start from scratch. If a given contract form works for one case, it's reasonable to expect that it will work for analogous cases (where "works" means "has the expected outcome in case of legal dispute"). Rental agreements are exemplars of recycling of contracts which has worked before.
A recycled contract can fail for two main (and related) reasons. First, the legislature may change the law – for some political reason, it may be decided to forbid a certain condition in a tenancy agreement. Second, appeals courts may "discover" that a condition really has a different effect that was assumed (e.g. which words does "knowingly" refer to). This can motivate post hoc or preemptive rewriting of contract templates (where the lawyer sees a risk in using the old language but where the courts have not definitively handed down a ruling).
There are various principles of legal interpretation which influence legal writing, generally summarized in a Latin expression such as Expressio Unius Est Exclusio Alterius, meaning "the mention of one thing is the exclusion of others". The practical effect of that canon of interpretation is, the more explicit your list, the less likely a novel situation will be already covered. For instance, if your present a contract that forbids passengers from "possessing weapons" on the boat, you haven't defined "weapon", so that is left to common sense. If you define "weapon" as "pistol, rifle, shotgun, explosive, poison gas, knife, flame thrower, sword, bayonet, brass knuckles, nunchuck", you run a risk that your list failed to include death-ray (a new technology). The risk is that in adjudicating the contract, the court will decide (invoking contra proferentem) that as the author of the contract you did not intend to exclude the death ray, because you could have included it in your list but did not. (It's not guaranteed that the court will exclude a death ray, but there is a risk). In other words, too much explicitness can work against you, in case there is some slightly different scenario that you did not anticipate.
There is a distinction between an actual ambiguity which is a property of language, and vagueness. A clause that says "drive a car or truck owned by a competitor" can be interpreted by the rule of English as meaning "drive a car owned by a competitor or a truck owned by a competitor", or "drive any car, or else a truck which is owned by a competitor" – this is a linguistic ambiguity. Linguistic ambiguity is more easily solved and correspondingly should be more vigorously eliminated. Trying to micro-define "computer" is more an exercise in imagination (does it include smart phones, smart watches, your car's ignition system?).