I had a very specific issue recently.
I had a Win 10 machine that I wanted to upgrade (motherboard, CPU, RAM, etc.). In order to ensure I wouldn't have issues with Windows reactivation on new hardware, I logged into my MS account so that my machine and the Windows key are registered there and I could easily reactivate it.
After the hardware upgrade, I couldn't get into Windows anymore! Due to the hardware change it would not ask me for my password, but ask me to setup a PIN. But in order to setup a PIN, I needed an Internet connection. Due to this being new hardware, I didn't have any drivers installed and network wasn't working so I was stuck.
Even after disabling the PIN requirement with some magic, it would still ask me for my password which it couldn't verify without an Internet connection. I tried using WinRE and the installation recovery to access the registry, but since I have a RAID-1 setup and those tools don't have RAID drivers, I couldn't access any OS data from the outside either (e.g. to change registry entries).
After 2 days of blood and tears I finally managed to get it working. I ran the recovery mode of a Windows installer from my USB, side-loaded the exact RAID driver I had been using in the OS from my old motherboard (which luckily worked on the new one). After gaining access to my RAID array, I made a copy of cmd.exe and named it utilman.exe or something like that. This allowed me to boot back into Windows and by pressing the accessibility button, I would get a Command Prompt window. I created a temporary admin account with all privileges and no password. Finally I could log into Windows and install the LAN driver! Yay!
But this actually wasn't the end of it... My ISP has some weird issues and I think they keep assigning me banned IPs from time to time as I had issues logging into my MS account a week earlier as well. (I also have issues with some other websites and keep getting captchas often.) I was able to circumvent the issue by connecting to my phone's WiFi hotspot at that time. And this time I had to do the same. While on normal LAN I simply couldn't log into my MS account.
Even though I lost two days on this, at least I didn't have to nuke my Windows installation. It's a complex setup for development and it would have taken me at least a day and a half to install everything. Not to mention the user data I have there. I had backups and everything, but it's still annoying. This is part of the reason I use RAID-1 in the first place (I had my OS SSD die.)
So yeah, Microsoft can stick its stupid MS account requirement up their ass for all I care.