For your own sake.

The other reason is because of

You cannot load any save files that you've saved in experimental in EA.

So if you do opt into experimental, you try it out and you're like, ah, it's not for me.

You will not be able to load that save file in the early access branch.

You cannot load a save file that is created in a newer version of the game, essentially.

You can load save files made in older versions, but you can't load them in newer versions, essentially.

So that's the other reason why it's really important to back up your save files before you try out experimental.