I've only played PC games which have leaning, and I must say it is a welcome mechanic. It's actually a much more realistic form of cover, rather than popping your whole body out of cover to take a shot. Rainbow 6 games are a good example of this.
Before the Vegas series, you could line up to a corner, and peek out of it to take your shot, just exposing your upper body. Quicker, more precise, less risky. Then came the Vegas series which introduced cover system, which takes you ages to pop out and take a shot, especially if you're in heavy armor. In multiplayer, it's just not worth it, gets you killed, and you soon ditch it, and only use it to use the 3rd person view to scan the area without exposing yourself at all. But taking shots from cover is suicide.
Why would a trained specialist throw his whole body out of cover to take a shot anyway, it's just stupid, and doesn't really go with the Rainbow realism - especially when you shoot from your less dominant side, huge awkward swing of the body into enemy line of fire. Why would an agent do this? You'd think they would learn to switch shoulders, heck I even learned to do that while playing airsoft. Having said that, it's still an awesome game, nobody forces you to use the cover system.
Phoenixmgs said:
Leaning is more useful in the open than it is leaning around corners.
Honestly I've never tried this, but I feel it could be somewhat limited for my use, except for really fine tuning, like with a sniper rifle/DMR. Maybe with consoles it makes sense, but I've trained myself to strafe rather than tap the left stick for finer control, or a mix of both. Since I've always thought of leaning as a "expose less of your body" mechanic primarily, it just seemed weird to lean out in the open.