Community folder is where all the addons or ‘packages’ are placed. Examples are community made liveries, third party sceneries/aircraft etc.
Often times these packages aren’t compatible with the latest patches released by Asobo.
So to ensure your sim doesn’t crash or misbehave when installing the newest patch, they’ve recommended to move these addon folders from the community folder to a temporary location and keep the community folder as it was when the sim was in default.