Noob question - GA Home Page vs Audience Overview

Hi Folks,

Very new to Google Analytics, so apologies if this is obvious. On my GA Home Page I see this which makes it seem our number of user visits dropped off a cliff in early September:



Audience Overview of users for a similar time frame looks like this:


Obviously I'm looking at two different sets of data here - all I want to know is the number of user visits per day, so which do I use?

Thanks for any responses,

Regards,
Rob