The downsides are, well, you have to actually run the tests, and it's harder to ensure the tests are actually providing meaningful coverage.

If you are at all worried about coverage, try Devel::Cover, it is amazingly helpful. And my personal recommendation is not to read the documentation that comes with it first as it just confuses if you are unfamilair with code coverage tools (as I was). Instead, i recommend just installing it, and running it on one of your test scripts, once you see the output, it will all make a lot more sense.

-stvn