As far as I can tell, DarkPlaces does not use this.
Is gl_ztrick necessary in the modern world? Does make anything significantly faster?From planetquake.com/console
If this toggle is enabled the game will not clear the z-buffer between frames. This will result in increased performance but might cause problems for some display hardware.
Although I don't have any problems with it, I've read that some people have issues with it with, say, those Intel Integrated Media display adapters.