This one is pretty, but what's the point?

.

It's a cute way to get a palette for something but otherwise it's just something trendy to post. I saw a blog that literally just posted pictures of waves that they did this too.

I've never seen it on Tumblr but I have been doing this on colourlovers.com for years

The purpose of it is because once you sample the colors you have a good set that you can use

for whatever graphics you need to make. Those colors will appear in harmony with the image already.