Taiko forces you to pay attention to a lot of stuff at once (at least if you're playing fullscreen on a wide monitor) on fast songs with high AR. You can't just look at the left side of the screen, or you won't know what's coming, but you need to be focused on it in order to hit notes accurately (unless you know the song well). I'm guessing once you get better it's less of a problem (I'm a terrible taiko player, but one of the reasons I don't play it is because it bothers my eyes and I find it really disorienting).
It may be different for others -- I'm just sharing my experience. It is a great way to train your peripheral vision, though.
It may be different for others -- I'm just sharing my experience. It is a great way to train your peripheral vision, though.