Back in High School I managed to be pretty aware of how much I needed to learn to find balance. Had a loooot of friends who were deep into WoW and would play every night, keeping themselves from healthy amounts of sleep and generally not doing homework or studying. Obviously education isn't the only metric of success, but they probably lost a few solid opportunities thanks to it, while I generally stuck to playing single-player console games exclusively on the weekends.
It's all about balance and moderation, as with everything. Too much of a good thing is always bad, and I tend to stay far away from games that force you to be deeply involved on a daily basis to have fun (MMOs, MOBAs, mobile games, multiplayer in general). Some people make the balance work with those games, but I'd rather not fight those urges and social pressure.
