You may want to use Shazmo's consise references to Federal Law and State Law . Atlantic City Electric Co. v. When the litigation on the merits is complete, leaving only the execution of judgment. The subject matter jurisdiction of appellate courts is limited to cases with final judgment, litigants may not consent to an appeal without final judgment. New York state courts allow appeals in many situation without final judgment.
Judicial order preceding final judgment all become appealable upon final judgment.
The Rational for Finality Allowing the case to go up and down the courts might undermine judicial management of litigation. Appellate courts presume that the trial court judge make the right order more often than not. Allowing interlocutory appeals only saves judicial resources if a mistaken order is reversed. If litigation proceeds after questionable order, the record will help the appellate court determine what effect the order had. Otherwise the appellate court would have to speculate on the implications of the order.