With the very low amount of recoil produced by the .223, the 3 round burst is excellent out to about a 150 yards. It is definately a tool for CQB. Opposed to full auto which will empty your 30 round mag in about 3 seconds.
As the close ranges, imagine hitting someone in the lower chest with the first round. The slight amount of recoil will drive the barrel upwards slightly as each additional shot is fired. You end up with 3 bullet holes relatively close together. This causes massive damage to the body.
The three rounds are fired off VERY fast, it isn't like a 1919 low cyclic rate machine gun. Depending on the rifle (the kind of buffer, weight of carrier, gas tube, lubricant, barrel length, ammo used, spring weight, auto sear delay, firing pin weight, ect.), it may only take a quarter second for all three rounds to be fired.
Full auto would really jack someone up, but the controlability goes down, and you use a lot more ammo on one target. Full auto is excellent for suppression fire or shooting into heavy brush (just like in Vietnam spray & pray).
There are trigger setups which give you SAFE, SEMI, BURST & AUTO. That way you could have the best of both worlds.
All features have their uses, not all are for shooting at paper. If I had the money, I'd do the 4 position system.
I find it interesting that any "newbie" who asks questions is a troll. Jesus, Not everyone is a self proclaimed know-it-all.
-Steve