Movies are movies and mostly NOT like real life! so it would only be practical on short ladders or that are at an angle of repose much less than vertical.

In movies they generally use what is known as an air brake descender/decelerator that uses a very thin but very strong steel rope attached do a drum which is partly is conical thus changes the gearing for the paddles as the wire rope gets pulled off, thus speeding up the paddles until air resistance acts as a brake as the cone gets smaller thus slowing the person for such shots on silly long ladders,

Air brake descender/decelerator (old technology despite what is said in the video)
http://www.youtube.com/watch?v=6thS31pvQLQ

If you have ever been on vertical ladders that are attached to building and structures, you will know the vertical uprights that the rungs are attached to are much thinner as they are solid steel or alloy, meaning you don’t have the inherent friction you get from stepladders which have much thicker vertical uprights that are hollow and placed at an angle less than vertical, also ladders on buildings are seldom just attached at the top and bottom unless they are very short, at all other times the vertical uprights have “stand-offs” which attach the ladder to the building/structure which allows enough room to place your feet on the rungs without hitting the wall or allowing you to put the lower half of one leg behind the rungs (between a rung and the wall) so you can use the back of one knee to lock yourself in place to rest, this is the point where you proposal fails, as the “stand-offs” behind the ladder uprights or at the sides would rip your hands from the ladder as you tried to slide down, thus guaranteeing your demise at the hands of gravity from high ladders as opposed to it just hinging on being shot while moving down the same high ladder.

But if you are silly enough to present yourself on a tall open unprotected structure like a mast (unless you are taking >1200m shots with plenty of your guys between you and them) then it’s perhaps more a problem of the tactical shortcomings of your choice of position rather than the shortcomings of ladders. ;)

Anyway, its mostly tactical safer to fall/drop one floor than to use a ladder IF you are suddenly exposed, even IF you could slide down “short ladders”
the fall from the roof of a building that equates to 4.45m is ~ 26% from running/walking while standing up, if you are prone and move slowly to drop of the range is >15% <26% damage often being around ~ 20% but with a much fluctuation than the former being in the range of >25.5% <26.5%, a 12.5m drop is ~ 90% damage, while a second floor drop from e.g. the top of the accessible roof of the “unfinished” type buildings is about 61% damage (can be as low as 50% if you are prone), or if you use the topmost floor/roof (where there is a single short ladder) and you drop to the immediate floor below damage is ~ 10% if you run/walk off it, and as low as 0% if you are prone and do an evasive role off it.

what is perhaps needed for between adjacent single floors or low roofs, is a set-piece animation (like that of mounting a ladder) that can be invoked at the top of short ladders/floor/roof edges from either a crouched or prone position, that lowers you over the edge or through the hatch, before you select release to drop.

Editing:
because the use of “~” to denote approximately screws up number formatting i.e. “~10” vs. “~ 10”

Mass closing ancient tickets with no activity for > 12 months; assume fixed or too trivial.

If this issue is still relevant in current dev build, please re-post.