I can think of a case. If you have your data in a high performance data store (such as SAS SPDS), you might want your SAS programs to not move scratch data out of that environment during processing -- a move that can introduce delays due to cross-environment latency. So you might define USER to map to a scratch location in the database environment and allow your one-level names to resolve to that.

When that part of your processing is complete, you could reset the USER option so that WORK is used again.