There is too much focus in this discussion about low memory situations. You want to avoid those as much as possible. Set reasonable ulimit for your applications.

The reason you want swap is because everything in the Linux (and all of UNIX really) is written with virtual memory in mind. Everything from applications to schedulers will have that use case in mind. That's the short answer.

Memory is expensive and storage is cheap. Even if you have 16 GB RAM in your box, and perhaps especially then, you will have some unused pages. Paging out those and utilizing more memory to buffer I/O will give you higher performance under most normal circumstances. So having a little bit of swap should help performance.

For laptops hibernation can be useful too.