This is a setting that allows you to change whether you are notified of mod preview updates for each mod that uses Main and supports the feature. Upon detecting that a new version is available for download, typically, a simple notification will be displayed at the top right of the game, you should only ever get this once per game session for each mod. For every mod with preview update checking enabled, regular update checking must also be enabled for the checks to occur at all.
In order to check for updates from NeonOcean, the mod will look for a file located at dist.mods.neonoceancreations.com/mods/latest.json, this file will be checked 15 seconds after a game session is first started, then once every 30 minutes.