When clients upload Information to a Secondary Site MP, that Information gets consolidated, compressed and then sent up in the hierarchy by ONE single file, in order to minimize WAN issues.
However at standalone MPs each small Client communication is being sent up using one little file, resulting in many little packages consuming lots of unnecessary WAN bandwidth.
That prevents us from getting rid of our secondary sites even though we urge to do so, i.e. because they caused critical failure when updating to ConfigMgr 1511 (classified by Microsoft as known Bug)