From andre.romcke@ez.no:

1. Multi upload
   Adds additional 4 ajax requests on every content view you browse, to check your permissions proactively.
   This is especially noticeable in development where requests are expensive, but it will also have an impact in prod.

Locally here this means (on 2011 macbook):

• Before: 21 ajax requests in 4.5s
• After: 25 ajax requests in 5.5s

Requests amount can be limited to one with batch permission checking. It requires changes on both frontend and backend.