What is it? Auto-Maintenance does a "variety of things" which Microsoft won't elaborate about, and you won't find any information about anywhere. When does it happen? Anytime during the day when you try to work (unless you leave your computer on over-night, like everyone with a laptop that's not connected to the power most of the time does...). The "Action Center" user interface doesn't give you an option to disable it, and people on the net would advise you to go to a "Task Scheduler" and disable it there. And you do, and guess what? 2 Minutes later windows enables it back without telling you.
So what you'd say, sure - just as much as I like to change car oil every 2 miles while on a road trip, I'd like my laptop to spike its CPU usage with odd services, and spend hours plowing through the hard drive doing who knows what, rendering your own processes and software helpless as they try to access IO. I mean, who's hardware is this? Yours or Microsoft's? Who decides when and how to use it and spend its power? Is it really that hard to open a web-page?
Auto-Maintenance kills laptops, and there's no way to disable or avoid it - so the only thing left to say is: Thanks Microsoft for truly - the worst OS you've ever created. I own several PC-s and laptops and I wish those were all Chrome or Mac now.