Putting an & in front of your sub calls doesn't just disambuigate between builtin keywords and functions, it also has a number of other specific meanings, one of which is to ignore prototypes. (See perlsub, IIRC.)

If warnings complaigns without the ampersands, it normaly means that you're naming your subs the same as perl builtins, which strikes me as a really bad idea, except if you're very much doing in on purpose (IE overriding the builtins).

(The only time I ever use the ampersand sigil is when I'm taking sub-refs, or (very rarely, indeed) using the "goto &func;" magic form (which calls a sub with the current contents of @_ and replacing the call stack instead of adding to it -- it's mostly equiv to return func(@_);, unless somebody (the debugger, most often, in code I'm writing!) looks at the caller() info (But I digress, often and verbosely.)) (I'm not counting the && logical-and operator, I said ampersand sigil.)