Transparency has always been an issue for Roblox, especially with semi-transparent Parts behind other semi-transparent Parts.
Glass also hides Terrain water, which is both good and bad. For places with water I just use SmoothPlastic or Ice for windows if I need to see the water.
A ‘nice’ use of the hidden water is you can make a boat for Terrain water that has an interior or sits deep in the water and put a Glass Part with Transparency .999 to hide the water that’s rendered inside the boat. It doesn’t work if the water is deep and the player needs to move around in that space because they’ll swim and if the camera is below the glass and above the water it’ll render.