When working with very large PowerPivot files the Excel autosave will make your PowerPivot very slow on moments it does its autosave. You can disable it for this single workbook (remember to save it yourself from time to time!)
Go to File ->Options.
Click on Save and uncheck “Disable Autorecover for this workbook only”.
This one is ofcourse on your own risk 🙂 but it saved me a lot of annoyance every 10 minutes.