But then you could just stand up! Like if you back up or sidestep into a tree and stop moving as a result, once you realise you're against a tree you just move round it. It should surely be the same thing here - once you realise that you're up against some terrain you can't crawl over, you have the option of just standing up, and in your own time, or even going round it.
The problem is it's not really possible to reliably tell what will trigger it and when. You may want to get as close to said terrain as possible for cover, especially if you're dealing with some narrow angles, but the added distraction of wondering what may inadvertently trigger what should in many cases be a major tactical decision (ie. do I stand up now and risk exposing myself or not?!) isn't what you need at a critical moment!
It's never an invisible barrier that you're up against, just one that you can't tell what the effect will be of on your guy. Makes way more sense to just have the hassle-free option of standing when necessary. If you ask me having your guy suddenly stand up when you're expecting to inch sideways is a major immersion-breaker!
Died a few times last night trying to nail a particular avenue of approach only to be suddenly completely exposed if I inched the wrong way!
Got to say I'm not convinced.. :S