My primary use case was magisk to enable taking screenshots from otherwise protected apps. Was living in China for almost 7 years, and even though I speak it quite alright, reading is a whole other level. And there are quite a few apps there that I had to use on a regular basis that had this damned flag_secure enabled so I couldn't otherwise take screenshots to run them through a translation app.

The second one was system level adblock, since the alternative is for adblockers to install themselves as local VPNs routing traffic to 127.0.0.1; however being in China meant I actually had to use a real VPN to access the free internet, and I certainly didn't want to choose between ads or privacy. The latter still applies; I'm using a VPN on most days.

Lastly, being able to use magisk also gives me access to some advanced security apps such as Hibernator (freezes apps, meaning they are basically uninstalled and reactivated on press, so they can't use data, don't get updated etc.), Storage Isolation (lets you configure on a per-app basis which folders it might access), App Ops (advanced permission management, which also includes an ignore function that acts like as if a certain permission was granted, but would feed random data or zeros to the app).

Being able to uninstall everything including system apps is also nice, though that can still be achieved with adb. Browsing root folders when looking for specific data is also nice, but I used that twice in about 5 years, so it's probably not essential.