Away from having the choice of enabling it or disabling it for your game, Some games like SS13 take heavy use of some features that require's HW Mode to be on for it to work correctly,
Some stuff like Lighting can sometimes not work in software mode which could result in players disabling HW Mode to cheat in games just like here : https://github.com/MaxIsJoe/TWC/issues/9
I think a simple function that can be called when the player logs in or something like that can be useful for games that heavily need HW mode to play.
(a bad) Example
Login() client.ForceHW = 1
1 forces the client to run Hardware Acceleration and 0 disables it.
EDIT : please ignore the example code, it's probably horrible and using <//code> made it look even worse.