On IRC and here at perlmonks, I often see people get "corrected" when they call their functions (theirs, not Perl's built-in functions) with a leading ampersand. I'm not talking about using &foo, I'm talking about using &foo(...).

What's the problem? I don't believe people are really concerned that these beginners are avoiding the prototypes of their functions, because 95% of the time, I also hear "don't use prototypes". So what's the problem with calling user-defined subroutines with an ampersand? Yes, it's optional, but it's not detrimental.