AFAICT pass just calls out to gpg; so the answer to your question is, "It does whatever a bare gpg command would do". If you have gpg (or more specifically, gpg-agent) configured to ask for a password every time, using pass will require you to enter in your password every time; if you have gpg-agent configured not to ask within an hour of the previous password, using pass will cause you not to have to enter the password more than once an hour.
And of course, if you've just entered your gpg password to decrypt an email with GPGMail (Mac Mail PGP plug-in), you won't have to enter your password to decrypt a password, since they're both using gpg behind the scenes.
