The original idea of the "nofollow" attribute was for blog comments spammers. Now Google requires that for paid links.
In addition it is commonly used if a site's navigation is screwed up and cannot be fixed without it being redesigned.

I have a personal blog and I do not use the "nofollow". I moderate the posts.

And about PR juice: If we all start keeping the PR for ourselves, there will not be any PR see on the web.

At last: I am against nofollow, and I implement other legitimate methods instead.

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