What does it take for you to reblog something?

I’ve been struggling with this lately.  Reblogging is considerate at best, and downright annoying, at worst.  There is some mutual benefit to the process: I reblog you, people who don’t follow you see that you were the source and perhaps they start following you - while simultaneously, my blog gains free content that you went through the effort of creating and posting.

Three times in the past week I’ve reblogged something, and each time I felt dirty for a different reason.

1. This instance from today, where I reblogged mayjah, bothered me because I’m fairly certain that everyone that follows me on Tumblr already follows her.  It was essentially a “retweet” and I added absolutely nothing relevant to the original content by reblogging it.  Why did I feel like “hearting” it wasn’t enough?
2. This instance, from yesterday, was a reblog of a reblog of myself!  This one arose out of what I see as a limitation of Tumblr.  I wanted to respond to the questions posed by Bailey in her original reblog, but there was no way for me to publicly respond other than reblogging it again.  If Tumblr had some sort of easier public communication system, that wouldn’t have been such a problem.  I could’ve simply commented on Bailey’s reblog (if she had Disqus comments configured), but then not everyone would have seen my answers.  Maybe that doesn’t matter?  Why did I feel like anyone even cared about her (likely rhetorical) questions, or even more so, my (serious) answers.
3. This instance, from a few days ago, was a “chain reblog,” which is perhaps the most annyoying type of reblog.  This phenomenon harkens back to my previous point about Tumblr not having a good public communication system.  Everyone wants to chirp in with their thoughts, but then you end up with a nasty chain of reblogs.  You’re constantly having to scroll up and down and trace imaginary lines in your head to figure out who posted what, etc.  It’s frustrating and provides for a bad user-experience.

What do you all think?  Is it about sharing someone elses awesome content?  Is it about joining in an ongoing conversation?  Is it both?  What makes you want to reblog something?