I'm pretty sure I get the jist of it, but want confirmation.
Update.zip allows you to update system files (like installing/upgrading a custom rom) without damaging any user data/apps/settings.
Nandroid restore wipes all user data while installing a custom rom. Its basically a backup of the dev's device.
Rom.tgz... well, tbh, idk wth this is or does.
Sbf allows you to install roms while wiping all data, even group 42 which is where the motorola M is stored for pre boot animation image.
Someone care to confirm, correct, and/or fill in the missing pieces for me?