Andy Mallon explains why you should never shrink tempdb data files:
I recently wrote about growing, shrinking, and removing tempdb files. In that article I explained that SQL Server won’t move a page that contains an internal worktable object, and thus trying to shrink tempdb files can be futile. Today, I’m going to explain how attempting to shrink tempdb files can actually be harmful.
Andy has good advice for tempdb here. Shrinking other database is generally bad but sometimes necessary; shrinking tempdb can lead to all kinds of problems.