Although this question (thankfully) doesn't come up that often, it is important nonetheless: what consequence (if any) is there to a personal injury claim if the plaintiff pleads guilty to a crime?
The answer depends on the nature of the plea, as well as the nature of the crime.
Thus, for example, pleading guilty to a traffic violation of making an improper turn may be admissible in a later auto accident case arising out of those facts. See, e.g., Ando v. Woodberry, 8 NY2d 165. On the other hand, if a party pleads guilty to a felony, that plea is no different - at least from an evidentiary standpoint - than if they had been convicted after a full criminal trial. And since the burden of proof in a criminal proceeding (beyond a reasonable doubt) is heavier than that in a civil proceeding (preponderance of the evidence), the party pleading guilty to the felony will effectively lose the right to contest that issue at trial of the negligence case.
This rule is part of the larger doctrine called "collateral estoppel," or issue preclusion, which in general terms means that once an issue has already been fully litigated, that party will not be permitted to re-litigate that issue.
Naturally, this rule promotes judicial economy, and provides some finality to judgments.