What are the factors in weighting whether to disclose substantive evidence vs. using it for impeachment at trial?
In an adversarial system (such as that in the jurisdictions in the U.S.) the surprise factor is disallowed on trial.
I am not knowledgeable on the procedural exceptions, but generally speaking the documentary evidence (including deposition transcripts) has to be filed during the discovery stage of proceedings. A discovery deadline is set up during case scheduling, and extensions of that deadline have to be requested via motion.
There is the slightly related concept of sequestration of witnesses whereby inconsistencies may serve to impeach a witness's testimony, but that is different than withholding from the jury any pre-existing evidence that a plaintiff would like to be considered on trial (whether for impeachment or otherwise).
Also, it is in the injured party's best interest that the jury get to see the evidence rather than have it merely rely on a witness's reaction of surprise. The wrongdoer's lawyer will try to confuse the jury and thus outweigh the jury's perception of a "surprised witness", but that attempt is likelier to fail if the jury has the evidence with which to compare the witness's testimony at trial.