My goal is to add user data to my website community. After reading some items, it seems like forms modules add user data just like registration modules. I do understand there is a difference between them. But it is not clear to me. Can someone explain their functional differences?

I know I want to ask questions in clusters, which points me towrds the purchase of a forms module. But, it seems like the forms module will also do registration. Is there a situation where I would need both the forms module and the registration module?

thanks