This is *indispensable* for developing in Perl for me! If I have no idea what's going on, I'll often work with the debugger. But if I've got a pretty good handle on what the script should be doing, I can throw a quick debugging comment out there and many times it saves time over stepping through the debugger--and finding those bits of code that just don't work the same inside the debugger (it happens).
While I'm working out the details, I typically dump out a value with a smart comment, and then exit the program.
One caveat for some who might find this a stopper, it's a Source Filter. If that doesn't bother you, it's a great tool as an alternative to not have to call in Data::Dumper everywhere and then write the print statement.