Xbox One troubles

I've had some troubles from time to time with my XB1, as with any hardware I'm sure, but there are two in particular that bother me. Today I setup ME: Shadow of Mordor, and after installing etc. I booted the game and saw what I assume is the loading screen, but nothing happened for a few minutes, and then I was sent back to the home screen.

The most reasonable suggestion I found was that the XB1's default power state didn't actually turn it off, but into a sleep mode to boot quickly. As a consequence, the RAM may have residual data that would eventually crash the system, or otherwise. Hearing this, I went to the power options, only to find the screen was black, except for where the cursor was.

I managed to fix this by shutting down my XB1, pulling the plug and then holding the power button for 5 seconds or so, then retrying. I'm really curious as to what this does, just pulling the plug did nothing, along with all the other suggestions I tried.

So I'm wondering:

• What might this solution actually do?
• What could be the cause of this problem? Is the residual memory suggestion plausible?