Actions have consequences, and in legal representation it may be malpractice,   Here is an example.  Say, for example that you have a robust asbestos practice, and in one of your many pending actions, you have one of many defendants file a motion for summary judgment.  You may not be sure whether there is any evidence against that particular defendant and sign a stipulation of discontinuance.  Is the stipulation binding, when a couple of months later you determine that there was evidence against that defendant?  Can you vacate?  The short answer is NO.  The longer answer is found in Hallock v. State of New York and in Charlop v A.O. Smith Water Prods.
2009 NY Slip Op 05911 ;Decided on July 21, 2009 ;Appellate Division, First Department

"stipulations of settlement are judicially favored and should not be lightly cast aside (see Hallock v State of New York, 64 NY2d 224, 230 [1984]; Matter of Kanter, 209 AD2d 365 [1994]). Thus, a party will not be relieved from the consequences of a stipulation unless there was sufficient cause to invalidate it, such as fraud, mistake, collusion, accident, or some other ground (see Hallock, 64 NY2d at 230; Daniel v Long Is. Univ., 184 AD2d 350, 352 [1992]). The party seeking to vacate the stipulation should do so with reasonable promptness under the circumstances (see Hallock, 64 NY2d at 231)[parties bound by a stipulation where they voiced no objection for two months following the execution of a stipulation]).

In Structured Asset Sales Group LLC v Freeman (45 AD3d 327 [2007]), the parties mutually decided to discontinue the action. The plaintiff received the proposed stipulation — which stated on its face that the discontinuance was "with prejudice" — and held onto it for two months before executing it (id. at 328). The plaintiff then sought to set aside the stipulation, a request which was denied by Supreme Court. This Court upheld the dismissal of the action (id.)."