I had a case of severe stuttering in the sim, where I had no idea what was causing it. I tried almost everything (including cranking down the graphic settings) but to no avail. And no: it was not a setting in the graphics. It happened after an Update to the sim (can´t remember which, SU5 maybe?) Before it ran perfectly fine. So instead of deactivating/deinstalling a ton of things in Windows and each time testing if it was gone, I decided to save time and make a clean new install of Windows to test the sim then on a naked Windows. Sure enough the sim ran smoothly again. No idea what caused the problem. But it also meant reinstalling the whole sim with its approx. 130gb. That took me 4-5 hours. But for some people it can take 2-3 days(!) because their Internet connection is fast enough for the sim, but not fast enough at loading huge amounts of data. In my case most of the sim was sitting on its own SSD drive and only needed to be recognized by Windows again. Why not make an Installer that checks what already has been loaded, and then only loads what is missing. Or make an installer for reinstalling after a Windows reinstall. Windows is not perfect, or often drives just get too small. For a lot of people this would be like a gift from God. Just a suggestion/wish…
A large chunk of the sim is installed in your Packages folder, including downloaded Marketplace and Community add-ons. MSFS prompts you for where the Packages folder should be located when you first install the sim. If you backup your Packages folder with all of its subfolders and point the installation to that location, there is not that much to download.