Each Office 365 user generates between 12 and 20 persistent connections. Each connectivity option deals with this challenge in different ways. Tests include DNS resolution, DNS resolution and file download times. Catchpoint research compares results between appliance-driven versus cloud-based direct-to-Internet deployment. The amount of time it took to establish a connection between the client (Catchpoint node) and server (SharePoint) was tested. It took time to download a 2MB file (WebEx player) compared to the time it spent to resolve the domain name of the host.”]
Source: https://www.bankinfosecurity.com/whitepapers/adopting-office-365-without-pains-w-3170