Having a chest rig, instead of an underarm rig, would come in handy if wearing a pack, or if in an aircraft seat that is armored (since the armor goes up on both sides of you, it makes it difficult to move your arm out to the side, to draw). It woiuld be nice, intight quarters, for the same reason - not having to move your arm to the side. So I can see it being useful or the military.
Non-military usage - looks kewl as hell, and really tuff, yo.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.