While there isn't necessarily a difference between them, there could be. I like dancing could mean that you get enjoyment out of dancing (doing it) or that you like to watch people dance, while I like to dance only means that you enjoy dancing (doing it). Having said that, in fact, there is hardly ever any difference between the two. After all, I like watching TV and I like to watch TV are the same. I like swimming and I like to swim are also the same.