Just bought some alien cams, in the booklet that came with them it says "never rely on a single alien placement to protect you from a fall" and it says that using them in horizontal breaks with anything other than a nicely curved edge isn't advised either - to prevent damaging the cable, with a little illustration containing a skull and cross bones!
Which is a bit suspect as i climb a lot in the lancs quarries.
The largest one (red) is rated to 10kn.
What do you think? Just standard disclaimer type stuff?
EDIT: forget that, DMM have nearly the exact same drawings and warnings.
The cables are a 7x7 cable which easily takes a set so droping onto it over a sharp edge is likely to kink it more or less permanently. I suspect that's what they mean. You'd struggle to break the cable as the rock would most likely pulverise or let before you actually broke it.