Crochet squares can be used for many different purposes like bags and cushion covers, but the main use for it must be a blanket I think. If you make loads of these squares and join them together, it will make the most beautiful blanket as you can see in the picture below. You can either choose to make every square in the same colour as in the photo, or choose to be adventurous and make every square in different colours to use up left over yarn you don't really have a use for.
I found the pattern on a blog called Mellie Blossom which has free crochet patterns and as a bonus it also has nice recipes on it. The original designer of this pattern is Susan Stevens of Eastlake, Ohio. The pattern for this square itself can be found here.