The UHD texture pack contains double resolution sprites, this is intended to make the scaling for UHD screens (4k+) look a bit more sensible.
The end result is that if you get the UHD textures on a 1080p screen you will effectively have less zoom range because all the sprites will take up more screen space.
So there are no new or changed graphics in the UHD pack, they are just bigger (and take up more memory which can be a performance hit for some systems). Some people like them even for 1080p screens and that’s totally fine as well.