When flying IFR with jet aircraft, the pilot has little discretion
unless specifically given by ATC.

A usual transmission is, United xxx, descend to 15000, and that's what
you do. On rare occasion, it may be a little looser, United xxx
descent at pilot's discretion, cross intersection xyz at 15000.

If you want a better feel for what actually goes on than you will ever
get via newsgroup, take a couple of United flights and listen to the
ATC channel - it can be much more entertaining than the movie at times.