Outside of rush periods, it's not uncommon on rapid transit lines (especially in more outlying areas on a given route - even in cities like New York and Chicago) for stopping at a station to be a complete waste of time.
While mostly common to cross-country passenger trains, whistle stops have appeared
even on rapid transit systems, including one on the Chicago 'L' system, where a train would only stop at the station if either a passenger on the platform signalled a motorman that they would like to board, or a passenger on the train would tell the conductor he'd like to de-board.
The reason they were called a "whistle stop" is because the passengers on the platform would be required to pull a cord, raising a mechanical signal that would give the motorman advance notice to slow down in order to stop at the station, which they were allowed to let go of once the motorman gave a blast of the train whistle to let them know he saw the signal and is stopping for them.
While this has become un-feasible in most places, late at night when transit service is sparse and undesirable, trips could be sped up by having trains skip stops like buses.
A motorman, if not signalled by a passenger pushing a stop request strip / pulling a stop request cord, and if the station indicates that there are no passengers on the platform (maybe by way of a passenger pushing a button that turns on a signal), the train could breeze by at a cool 55 m.p.h., instead of wasting everyone's time.
Of course, this idea really is half-baked since it would totally throw off schedules, quite possibly conclude in "train bunching" (much like "bus bunching") in the event that one train has to make all the stops, while the next one skips a whole bunch (especially because the train before it was stopping a lot and was late, and so the next train, running early, is getting to stops shortly after the passengers have all been picked up), and the practicality of it which is probably why we don't have any "whistle stops" on our rapid transit systems today. lol