SPW 2010 creates a new workspace for every connection to a library or folder within a library.Over time, you'll most likely accumulate a collection of workspaces you no longer use.
You can think of a Share Point workspace as similar to a Microsoft Groove workspace.
The whole point of SPW 2010 is to let you work on Share Point data even when you're offline.
It's hard to work on a document if all you have is the metadata.
It's nice to have other documents available offline, but not truly necessary.
Decreasing the number of cached documents can correct performance problems.