Hi
Note that every time you load a project, VP gets the data first from the vpj file which refers it to the data held in the cache, so the project loads faster. The vpj file does however hold details of the cache contents and if these are missing it would take time to find and regenerate them.
If the cache was to be automatically emptied every time you stopped work on the project, there would be a delay every time you restarted work whilst VP refilled the cache.
The caveat here is that if you have completed numerous projects that you don't need to go back to, the cache can contain a lot of unnecessary files which can slow things down.
If you have a project loaded then use OPTIONS | DISK/ Clean Unused Cache Files. as Borate suggests, to remove all these unwanted files leaving just the ones that you have loaded for your current project.
Nat