If you're someone that plays competitive games where framerates matter then, no, a 240Hz monitor is unlikely to be considered overkill. With that said, if you mostly play story/cinematic games and indie titles then you aren't going to get the best use out of the added quickness. Doubly so if you aren't rocking a particularly powerful GPU that can hit those heights, or playing on console, which at best can hit 120fps in certain games.