I believe that is where your personal settings and Sims are stored. There is another folder in that documents that you need to pay attention besides the saves folder and Mods folder. I for one ended up just nuking and re-downloading my game many times to help resolve the issue. If you start to be complex with Wicked Whims and Command Center and other scripted mods and such you will end up with some issues that will be able to be overcome but with some effort.
If you want some eye candy like Kendo's outfits and such you will be very safe. However like other things if you have mods that conflict it becomes a bit harder to work on. You drop the package or Script into your Sims4/Mods folder found in your documents (where you find the saves) It is basically that easy.
