So, here I am trying to figure out how to manage my assets on Sketch, and after going through the official iOS design library I've figured out some bits.

I've added a bunch of gradients I use regularly. I'll be added more consistently.

Tip: Delete ~/Library/Application Support/com.bohemiancoding.sketch3/ has a bunch of files you can remove when you feel like you've cluttered up your assets or palettes and shit.