The U.S. Marine Corps now allows battalion commanders to decide if and when their riflemen can wear less armor, and in what circumstances. Before that, only regimental or brigade commanders had that authority, and the new rule takes the responsibility down to a more reasonable level. Even though the marines tend to be more innovative, and use more initiative, in matters like this, senior marine officers have been putting off making decisions on the matter of how much body armor is enough. This is all part of an ongoing debate in the infantry community over how much body armor provides the right combination of protection and mobility. There are times when the troops have to move fast (as when chasing down a sniper). But the senior commanders are under a lot of pressure to keep friendly casualties down, so they tend to insist that the troops wear all their armor all the time. Despite this, some subordinate commanders look the other way when troops shed some armor temporarily to get some needed speed.
Recent protective vest designs have a quick release feature, that makes it easier to get the vest off, and back on again. The most recent design is much lighter, but covers less area. Some 500 of these new vests were supposed to be over in Afghanistan by now, for troops to test in combat. But the army procurement bureaucrats got cold feet at the last minute, and decided to delay the tests so that the new armor could undergo more studies.
This infuriates soldiers and marines, who point out that the SOCOM operators (Special Forces and SEALs) will sometimes go into action without their protective vests, and get new equipment very quickly. Again, that is done because completion of the mission is more important than covering your ass when a reporter goes after you for "unnecessary casualties."
Many of the troops are willing to take the risk, because they believe, for example, that taking down a sniper when you have the chance, is worth it. If you don't catch the guy, he will be back in action the next day, kill American troops. All this is another example of the fact that "victory" is defined differently, depending on what your rank is.