That doesn't make sense. The primary use-case (and traffic driver) for Tumblr is a social network for logged-in users, similar to Twitter but with some differences in the feature set.
The public blog network is a minority of traffic. If you've never actually been a Tumblr user, you won't have an understanding of the product at all.
The public blog network is a minority of traffic. If you've never actually been a Tumblr user, you won't have an understanding of the product at all.