Exclusive use is desired for both Binary and Text files. Binary files such as graphical resources, and some text files. Most everything can be merged later, but there are times where it's desirable to lock a file from shared use in the shared repo. Some files are simply more painful to merge than others...if you know that ahead of time, lock it. Also, some sections might be in for a big refactor (15+ year old legacy codebase) If you plan on a refactoring a few units, it's best to lock those to prevent merging issues. It simply puts a tool in the developers hands to let them decide when a lock will save future headache.
Community Edition user.