Which situations benefit from Perl's study?

I'm playing around with study, a Perl feature to examine a string to make subsequent regular expressions potentially much speedier:

while( <> ) {
    study;
    $count++ if /PATTERN/;
    $count++ if /OTHER/;
    $count++ if /PATTERN2/;
    }

There's not much said about which situations will benefit from this. A few things you can tease out of the docs:

• Patterns with constant strings
• Multiple patterns
• Shorter target strings might be better (takes less time to study)

I'm looking for concrete cases where I not only can demonstrate a big advantage, but also cases that I can slightly tweak to lose that advantage. One of the warnings in the docs is that you should benchmark individual cases. I want to find some of the edge cases where a small difference in a string (or pattern) makes a big difference in performance.

If you haven't used study, please don't answer. I'd rather have well-formed correct answers instead fast guesses. There's no urgency here, and this isn't holding up any work.

And, as a bonus, I've been playing with a benchmarking tool comparing two NYTProf runs, which I'd rather use than the usual benchmarking tool. If I come up with a way to automate that, I'll share that too.