Robert M. Gary wrote:
It's not necessary at a class C or B tower, those facilities are the IFR
facility for releasing departures. It is a nice thing to do at class d
towers as they have to get a release from the IFR facility.


I would believe that myself if I hadn't had several cases where the
tower controller forgot and didn't secure my IFR release from class C
airports.

The tower controller has automatic releases at class C airports.