This comes up periodically. The answer is in perlsub, if you omit the parens there is an implicit set of arguments passed which might not be what you want. I consider this a dangerous style because even if you know about the gotcha, the person after you might not.

Two other relevant notes. There is a promise that future Perl built-in functions will be lower case, so some people like using mixed-case function names. Also using the & is (IIRC) considerably slower than not using it.

Personally I used to use & all of the time, but now I never do. I don't consider the arguments either way particularly convincing on that. But I always put in the parens.