I clear caches at the end of game play if they are large in size, otherwise I leave them alone. For me, it's the compositor caches that get large and my game can freeze if the simCompositor file goes over 300k. (I minimize my game and check the stats while playing so I can save and then quit if the numbers get too high.)
The email and password problem requires you to reset Internet Explorer and tick the box to delete personal settings.
The launcher was created when Internet Explorer was the main browser; so even when you don't use it, Windows updates will adjust things and you must go and reset it.