Thread:Extension talk:GlobalPreferences/Could you expand on the difference between this and the default sharing of the user properties table?/reply (2)

The extension lets you choose which of your preferences are set globally and which aren't. So you can set your skin to be the same on all wikis, but have different watchlist settings on different wikis.

Using one global user_properties table works fine for most cases, but there can be some weird edge cases if, for example, one wiki has a preference hidden with $wgHiddenPrefs, and another doesn't. Or if two wikis have two different gadgets named the same thing.