Honestly the queue and schedule post options on Tumblr are extremely underrated. No other major social networking site has the ability to do that with the same ease as Tumblr does, and we've had them for like a decade now. They're fantastic features and Tumblr doesn't get enough credit for having them.
I'm actually willing to assert that Tumblr actually has some of the best site functionality:
- queue/schedule system
- tagging that doesn't interfere with the actual content of posts
- the ask/inbox system
- ability to make likes/following lists private
- ability to reblog posts multiple times
- the "Keep Reading" feature
- ability to easily post different media. AFAIK Tumblr is the only social media site that lets you post audio without it being a video.
- dash is always in reverse chronological order
the ability to almost entirely customize your home page is pretty neat, too
I could go on about this forever but I firmly believe that Tumblr is a remnant from a time before companies figured out how to efficiently monetize social media, and as such it's designed with users instead of advertisers in mind.
That's both why it has continued to have active avid users in spite of a lot of technical /policy issues, and why it hasn't been massively profitable.
I treasure this garbage site.