It was not unusual for an E-4 to have over 8 years of service before being promoted to Sergeant. This gave that E-4 several years to be used, and abused, and develop, and mature into the rank of Sergeant. That isn't happening anymore. The exodus caused by junior and mid-grade NCO's is accelerating promotions in those ranks at a rate unprecedented in the 15 years I have been in the army. This creates two problems that I see.
Inexperienced leaders tend to make more mistakes.
In combat that usually means more filled body bags. If I don't make it in 10 years, then I will get out. Furthermore, in many of the Combat Support, and Combat Service Support MOS's, it is not unusual to be promoted to E-7 between your 15th and 18th year in service. E-7, so people tend to stay there for awhile, those slowing down promotions. If these individuals don't see themselves climbing the ladder of success fast enough, they will move to an environment where they can.