Using local on lexical or package variables can be dangerous.

You can reduce that to:
"Using local can be dangerous."

See also Coping with Scoping. In short: don't use local on variables not mentioned in perlvar. Do use local on variables mentioned in perlvar.

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }