From the FIDE Handbook:
III.2.2 These Guidelines shall apply only to standard chess and rapid chess games without increment and not to blitz games.
III.4 If the player having the move has less than two minutes left on his clock, he may request that an increment extra five seconds be introduced for both players. This constitutes the offer of a draw. If the offer refused, and the arbiter agrees to the request, the clocks shall then be set with the extra time; the opponent shall be awarded two extra minutes and the game shall continue.
According to this, if I crush my opponent in a rapid game using all of my clock time except for a minute, then I can simply request an increment of 5 seconds for continuing the game (my opponent gets two minutes, but that will not affect the game due to his/her hopeless position). Is this fair enough?
There have been many examples where this rule could be used but wasn't, for instance, the Unofficial Chess960 World Championship, Carlsen could have requested an increment and tried to win the R + B vs R endgame instead of flagging. Why didn't he do so?