Let's say that matches 100 files. The rm command gets 100 complete pathnames from the shell: /somedir/otherdir/afile, /somedir/otherdir/bfile, and so on. For each of these files, the UNIX kernel has to start at the root directory, then search the somedir and otherdir directories before it finds the file to remove.
That can make a significant difference, especially if your disk is already busy. It's better to cd to the directory first and run the rm from there. You can do it in aif you want to, so you won't have to cd back to where you started:
(cd /somedir/otherdir; rm *)
There's one more benefit to this second way: you're not as likely to
get the error
Arguments too long.
(Another way to handle long command lines is with the