When it’s not drop-dead.
Let me explain.
I have a theory. If there is an important event that the piece of work needs to be completed for then the deadline will be hit. Take the printing of an annual report. It absolutely, definitely, no-questions-asked has to go out on time. All nighters are timesheeted. Everyone from the agency account junior to the receptionist is called in to proof-read. All the stops are pulled out to hit the deadline.
Then there are the other types of deadline. The arbitrary ones that are plucked out of thin air when someone makes a finger in the breeze estimation and sets a date with a pin in the calendar. These nearly always get missed. There’s no urgency. No reason why a manager can’t just push the launch date back a week or two. After all, no one has to make any compromises or sacrifices of features, functionality or ‘completeness’. There’s always more time to ‘make it a little bit better’. To keep tinkering.
What’s to loose? Nothing, apart from team morale, enthusiasm and work quality.
Beware the project with the arbitrary deadline.