[aur-general] When to use optdepends (was: AUR package q -- newbie)

It's not really clear to me when to optdepend.

Comments welcome. My idea is to use optdepends for things the user may want, but it's not obvious how to make them work, like a glue-library the application needs to use another facility, e.g. gpgme to use gpg, or ghostscript to produce PDF.