Well obviously has some applications, Mike Pannone seems to incorporate it in to his rifle curriculum. His class, as well as Bennie Coolie's provided enough practice were making braced, weak side shots around cover at 150-200m on reduced sized silhouette's wasn't terribly difficult. The reality is not every corner or cover is going to be optimal. Esp in an urban environment. Being able to deliver accurate fire to a reasonable distance and manipulate your rifle around the other half of corners or cover and keep your profile to a minimum isn't a bad thing.
With anything, it takes practice and time (and live fire practice) to do well. This is an area were red dots shine, as getting behind the dot and getting being comfortable is half the battle when it comes to practice. Once thats accomplished, things start to gel and it gets easier. As with anything, reps are key.
Realistically, a sub-optimal corner is going to present itself far more often then situations that require shooting under a vehicle or laying on ones back. Not saying those positions do not merit practice, but that I find a weird aversion with some to shooting weak/support side vs doing the sexy "urban" prone stuff.