Fwiffo: If somebody just turns on a chess program, it's easy to tell. For example, when a program comes to the end of its data base (human moves) it rearranges its position (switching to computer moves).
Also, it attacks in waves and makes anti-positional moves, though good ones from its perspective.
Most common is for a player to check a human selected move for tactical flaws.
An argument in favor of this is that it teaches strategy and eliminates ruining a good game through blunders.
However, it also eliminates the suspense that is part of the enjoyment of the game. So it's a choice between instruction and enjoyment.
I don't see how this is "cheating" but, in any event, those concerned about it, almost always seem to be poor players and probably would be better off concerning themselves less with witch-hunting and more with improving their skills.