Strict deadlines
In New York, the summons and complaint generally must be served within 120 days after the case is started. Miss it, and the court can dismiss the case against that defendant unless it grants an extension.
Mistakes can undo a win
If service is challenged and found improper, the court may never have had power over the defendant. That can mean motions, delays, and even a judgment, including a default judgment, being thrown out.
Proof the court accepts
An affidavit of service records who was served, when, where, and how. It is filed with the court and becomes the record that service happened.
Rules change by location
How papers can be served, and by whom, depends on the state and the court. In Manhattan, service follows New York's Civil Practice Law and Rules (CPLR).