Be more friendly to inexperienced users. What do I mean? Compare locate's output e.g.
$ locate
locate: no pattern to search for specified
$ locate -qsd
locate: option requires an argument -- 'd'
with, say, that of grep ...
$ grep
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.
$ grep -qsd
grep: option requires an argument -- 'd'
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.
In case you haven't spotted what I'm getting at, notice that failure to give proper commands to grep results in displaying information on how to get help. locate, on the other hand, does not. I tried searching for 'invalid option' in mlocate's source, but was unsuccessful, otherwise I would try a pull request.