I wasn't sure if this was a feature or a bug, but when holding Z and mousing over belts with an item in hand, the even distribution icon shows. This would be a nice feature to spread a load of items in your inventory onto a belt. Early game my inventory is filled with things like plates and coal that could be placed onto my bus.

The Z thing is a new feature of 0.17, but the even distribution icon showing was definitely not intended.

Early game my inventory is filled with things like plates and coal that could be placed onto my bus.

Well, thats what the Inventory Cleanup hotkey usually is for. It gets rid of these items, although it places them directly in the machines instead of the belts.

Would there be any other use case for distributing to belts?

I ran into this earlier and I don't really see a use case for this. To me it seems like a bug that should just be patched out.

I fixed the distribution to belts in version 0.3.3