is it a mac pro, or is this in the wrong forum and you're actually talking about the retina in your sig? if you're talking about your retina, you would need to contact applecare to get assistance to turn off the password once it's set so I'd think long and hard about whether you want to enable it.
Anyway, an EFI password will disable single user mode, and force you to type in the password whenever you want to access the boot picker. that's about it- there may be some other maintenance boot modes that it disables that I've forgotten.