I had to install a third-party defrag because sometimes the defrag for Windows at default settings wouldn't run as scheduled for Win 7 and 8.1 (as seen in dates indicating when the last defrag took place). I read somewhere that sometimes, something would make it appear that the system isn't idle, which means the defrag wouldn't run. In other cases, users boot up, use the machine, and then close it. I only realize something has gone wrong when the computer slows down considerably.
In another case, I decided to run the defrag manually, and it went on working for 16 hours, with something like a dozen passes, and it wasn't through. I stopped it, installed and used Auslogics, and it finished much faster.
With that, I decided to install and use Auslogics running quietly weekly, and following any prefetch layout required by the system plus minimizing problems with VSS. What I had to do to stop it from accessing the net was install Firewall App Blocker and add the files to the Windows firewall block list. For my machine, I used a free version of Sphinx Firewall Control (which I can't use for the other machines because their users are novices and don't know whether to enable or disable access for various apps).