I don't think it will effect performance. This needs to be tested. Alt tabbing will mess with some games, like screwing with textures and what not. Games like Skyrim.
I alt-tab a plenty in Skyrim and it doesn't effect my performance at all.
I just realised I have the stupidest name in the forum
Scarface and Assassin's Creed graphic suddenly gets blurry, too much alt/tabbing in Saint's Row The Third freeze the game.
Other games work just fine for me.
Wait, why am I doing this again?
Played Max Payne 3, finally at the very last part of the game, only need to shoot a goddamn plane with grenade launcher, was auto-saving right before I hit R2, then the electricity went out.
Corrupted data appeared.