Lots of people have reported having disk usage at 100% after booting Windows 10, and seeing CompatTelRunner.exe scanning a lot of files.
(See Anyone know what CompatTelRunner.exe is/does?)
Using procexp.exe, I found that the offending process was started from a scheduled task, namely, Microsoft Compatibility Appraiser, which is found in Computer Manager under Task Scheduler\Microsoft\Windows\Application Experience\ProgramDataUpdater. There are three tasks in that folder.
The description of the task says “Collects program telemetry information if opted-in to the Microsoft Customer Experience Improvement Program.”, so I suppose we can simply opt-out from the telemetry program and this should not run anymore. I believe that is in Settings->Privacy->Feedback.
However, Windows Insider machines probably require this to be on, in which case we can go about disabling the tasks in Task Scheduler.
While I do not consider this an ‘official’ solution, it alleviated the problem in my machines as far as I can tell.