If i createt a Level in Valves Hammer Editor i look into the Object Preferences for the Heigth. First i create a Player Entity(Height the same as the cbabe Model). The in Make a Wall Taler than the Player Entity. My thougth is, that the Player Entity is 1,80M Tall(In height Position = 72).
So the wall is 2,4 Meters Height. This is the Optimal Wall Height for maybe a Room.

In Quants it is(Grid=16(Checkthis in the WED->Preferences)

--- First Value = Height Position ---

32 = 2 Quants (0,6 Meters)
64 = 4 Quants (1,2 Meters)
72 = 4,5 Quants (1,8 Meters (If this Value changes, the Quants System fit to the Meters Values!))
128 = 8 Quants (2,4Meters)
256 = 16 Quants (4,8 Meters)
512 = 32 Quants (9,6 Meters)

EDIT:
Textures fit to this "Quants System"

This is my opinion about Quants...

cYa Sebastian