What the big deal with Adjustable Gas blocks?

[Eagle1899]

A good example is my "Recce" style competition rifle. 18" mid weight barrel, rifle length gas system, lightweight carrier, solid delrin carbine buffer, rifle length recoil system with carbine spring and a travel reducer(also of delrin, with a through hole), muzzle brake and a Superlative Arms gas bleed adjustable gas block. I run 77 Tipped Match Kings with a healthy dose of Varget. It ejects cleanly, locks back when empty, runs dirty and has the least amount of recoil of any AR I've set up or shot that is of equal weight.

 

[Eagle1899]

On the flip side... I have a 308 Large Format AR that has a two position gas block. Un-suppressed or suppressed. I changed from a rifle length recoil system to a carbine length recoil system. I had a custom heavy weight stainless steel buffer with tungsten weights made to offset the shorter spring and less mass of the shorter buffer. It now works great and doesn't destroy brass or bolt stops.