Custom Permission Level and Sharing Documents

In SPO I am creating a custom permission level with a copy of default Edit. In my custom level I am removing the Delete options, Use Self Site Creation, and Add/Remove Personal Web Parts. 

Users assigned to this custom permission level then can not share documents. Testing I have found that I need to have both Self Site Creation and Add/Remove Personal Web Parts checked/included in the permission level for users to be able to share with others who do not currently have access. I have looked online and can't find a explanation for this so was wondering if others had this same issue and if anyone could explain to me why these two setting affect sharing?

See Attached screen shots.