I think i know what you're after with the disguise stuff. Changing your appearance is actually super useful beyond just looking different. When you take on a drow form, you can really mess with goblin encounters, and going githyanki opens up some interesting patrol conversations. Something really neat you might not know is that you can actually trick dead bodies you've killed into talking to you if you change your look first, which is great for getting information.

The gear stuff is pretty interesting too since disguising as certain races lets you use their special weapons, like that githyanki greatsword with the extra psychic damage. If you're trying to get into tight spaces, switching to a halfling form works well, especially when you combine it with some size-changing magic to squeeze through gaps.

Playing as a female drow in the underdark is particularly useful, gives you some real authority with the male drow down there. Just keep in mind that anyone connected to you through those tadpoles will probably see right through it, and some story moments won't buy the disguise no matter what. Oh and if you're planning some sketchy stuff, changing your appearance before and after means you won't take the reputation hit, which is pretty handy