The only truth here is that you can't see beyond your needs. If you have a fairly open site, with only restrictions on core functions, it would make perfect sense to sign up for news, but not register to be a full member. If I just want to be updated with a newsletter, not take part in a discussion, I would prefer to drop my email in a box rather than a laborious sign up procedure, with another password to remember.
I like the way it gathers the emails for guests. But I would prefer to not have any automated emails sent. I just want to gather them to compose a HTML newsletter..