It is well known that the best practice says “One workspace per project”. Unfortunately it is not always possible to make it as the default solution, for various reasons (typical audience, etc.).
In Visual Studio 2013 the best practice made it into the product: the default Workspace Mapping is exactly one-per-project! In fact if you configure the Workspace for a new Team Project, you are going to get prompted to configure it:
After clicking Configure, you are going to map the Team Project root into a specific folder into your User’s folder:
It is definitely a good improvement, as it prevents the creation of a one, big, monolithic workspace which can take ages to download when needed, with all the related performance problems.