Think of it a little bit like a savings account for some of your data. AudiencePoint will store your data for you and can retrieve it anytime you want.
Normally what happens when you leave a provider there is a period of time where they keep your open and click data, but that period of time is short and difficult to access ( if you even can ). However If you leave provider "A" and go to provider "B", you can store that data in AudiencePoint. The open and click history is now accessible and available for when you want to do send-time optimization on provider "B", so when you land at provider "B" you aren't losing that valuable history.