If you think Tumblr is just a content aggregator, perhaps you’re not doing it right.
— Marc LaFountain on this.
Agreed. Tumblr does offer an intentionally basic feed-import feature that can aggregate your content from other sources. But that’s not what Tumblr is for — it’s just one feature. Most good tumblelogs don’t even use it. (If we really intended for Tumblr to just be an aggregation service, that feature would probably be much more customizable and robust, since we wouldn’t need to “waste” time developing everything that powers the rest of the platform.)
There’s not much value in blind aggregation: human editorial choices bring value among content overload. Sure, you can post your entire vacation photo album to Flickr, but as a casual web-acquaintance following you on Tumblr, I’m happier if you just pick the best 1-3 photos to publish here.
It depends on your audience: if you’re only being read by people you know well in real life, they might want to see all 75 vacation photos. But if you want your tumblelog to have a larger, more general audience of people who aren’t necessarily interested in seeing so much of your activity, you bring great value by showing editorial restraint.