How crisp a uniform is pressed, how well boots are shined (when we had to shine them, the new boots don't need it) placement of badges are all indicators of the effort someone puts in.
Uniformity also helps ensure a comradery, and team environment. Everyone looks the same because they wear the same uniform. The only way for a soldier to separate themself from the rest is either to exceed the standards, and encourage his teammates to do the same, or rock the boat, and hope he doesn't get thrown out.
The Army is about executing the mission, whether its unloading supplies at a warehouse in Texas, or going on patrol in Iraq. The ability to execute tasks is something that must be practiced.
A similar example can be found in the NFL. NFL minicamps open this week, and the players are practicing techniques, and plays every day in order to ensure they can execute when game time comes around.
It may seem silly to make a big deal about a badge not being 1/2 an inch from the top edage of a pocket, but after a while determining that 1/2 inch gap becomes second nature, and handy when the soldier is told to crimp the blasting cap 1/2 and inch from the end. no need to waste time and put life at risk by looking for a ruler in your pack.