Military combat is entirely different. You basically shoot until 1.) The bad guys give up or are all dead. 2.) You run out of ammunition. 3.) You die. 4.) Your gun stops running, (See #3)...... Which quite a few M-4's have done over the years. As far as barrels, the taxpayers can always pay for more.
In civilian use the cooler you keep a barrel, the longer it will last. Shooting a barrel that is too hot to touch will greatly accelerate wear, and degrade accuracy. Out here in the Summer it's all but impossible to actually "cool off" a barrel once you heat it up. Especially if it's over 100F and you're shooting in direct sunlight. A tool like this can really help keep things cooler than you could otherwise.
I'll admit I'm a little more anal about it than most. For run and gun, or full auto shooters something like this can really help. While I can certainly live without it, it's a nice gadget to have on hand. I just let it run while I refill my magazines, and it really helps keep the barrel cool. It's also nice to cool the gun down before you case it, and head for home. Not so much here, but in Illinois I've cased hot guns in very warm, humid weather, only to find condensation on them after I got home. This helps eliminate that condition.