Browser ate my post - I'll try to cover everything again, but won't waste so much time typing it out again, sorry.
The new tooltips can cover many item slots in inventory, especially when using the controller to navigate slot by slot.
For instance, the tooltip for a map has scale details along with a few other lines of information. Without any transparency, this just gets in the way while navigating around the inventory. An option to specify a transparency level or completely disable the tooltips (since i'm pretty familiar with what the blocks look like anyway) would be nice.
I think that only applies to the screen display of what the X (Crafting) and Y (Inventory) buttons do during normal gameplay, I don't think it actually affects the display of the tooltips shown when hovering over items in the inventory. I can test this later on today though, when I get a chance.