Benefits of creating a new workspace for each project in Eclipse?

Simply put, there aren't enough advantages to having a separate workspace for each project to justify it.

But here's something practical to consider: do you ever need to reference files or code from one project while you're working on another? I know I do that all the time, and that wouldn't be easy to do with isolated workspaces.

I make a workspace for every project, as Eclipse takes ~45 minutes to build my company's app and you cannot do anything useful while that happens (i.e. save files, change settings, do any sort of refactoring or autocomplete). I have multiple workspaces so I can use one while the other builds and vice-versa.