I think swap was mainly for older machines that didnt have a lot of RAM. When the cache was filled it would use swap space as memory to hold data. If you have lots of memory in your machine I dont think it would really need to use the swap space unless your running some hefty applications.
Windows has something similar to swap, virtual memory, but they just dont use a set space they use the empty space at the end of your drive. I could be wrong though, this is just what my understanding of swap is.