As a Roblox developer, it is currently too hard to use terrain for cliffs as optimization systems does not work how I would have expected them to work.This terrain wall you see here uses 20mbs of memory.
Mind you this is paper thin. Now lets rotate this 90 degrees.
This only uses 2.3mbs of terrain you can test this by setting a brick to 2048,2048,1 for the size and converting it to terrain. Try to rotate it so it is straight up and down and then flat for some reason the optimization system does not work the same and makes a vertical wall uses a lot more memory than a flat surface. If roblox could fix this, this would greatly and I mean greatly help my map that currently sits at around 630 mbs of terrain and due to this issue, it takes people like a solid minute to load.