Doing it on purpose to rest your cramp like the Fog is another thing completely.
Most FFs in pro tennis are indeed accidents. No sane player would risk getting called for it just to "cheat" one cm or two, especially considering the distance to the net in the first place. It's roughly 39 feet (11,89m) to the net. Making it an inch/few cm shorter might give you some psychological comfort but you wouldn't find any coach or player that recommended bending the rule as intentional strategy.
But playing with some buddy and you don't just touch the line but step a full foot inside the line or something....then we are talking