the changes that will happen with this is:
1.) The new launcher fixes every corrupt or missing file(s) in the client.
2.) The settings panel will be the same as before, except it will include a option to change the font in-game to a list of several fonts.
3.) If you make mods, and somehow mess your client up, you can simply press the button "Fix Client" in the settings panel, and it will begin repairing your client. However, if you do this, all mods that you currently have will be overwritten by the original ones.