I like comments where they give context that isn't otherwise obvious.  My issue with XML comments is that they encourage/require you to document obvious things, which introduces unnecessary boilerplate and duplication.  This can lead to even more confusion if someone forgets to update them when the code changes.

In this example, I think it is useful to comment that filePath accepts both relative and absolute paths, and maybe also the distinction between `*` and `?`.  It should be obvious that the purpose of Glob.Expand is to expand a glob, and that the IEnumerable<string> will therefore be the filenames that match - there is no need to repeat this in a comment.