Blood alcohol concentration is a huge factor in many drunk driving cases. This measurement of the amount of alcohol in a person's blood stream can help to indicate what types of issues the person might have with daily activities and tasks.
The effects of alcohol start long before you reach the .08 percent limit for driving. In fact, a BAC as low as .02 percent could lead to you feeling a bit lightheaded. At this point, there really isn't any change in coordination.
A slight increase to .04 percent to .06 percent can lead to you feeling a bit less cautious. You might also have some reasoning difficulties at this point.
From .07 to .09 percent, the real effects kick in. At this point, you are likely to have some difficulties with coordination and judgment. Self control is also lacking by this point. Typically, you will feel like you are doing much better than you really are once you hit this point.
After .09 percent, it is a very slippery slope. You are likely going to have blurry vision and loss of balance by the time you hit .13 to .15 percent. You can imagine how hard driving would be by this point.
By the time you hit .16 percent, you are likely going to appear sloppy drunk. Beyond this point, you face health risks, such as the possibility of going into a coma.
These effects of alcohol are one of the reasons for drunk driving laws. You shouldn't drive by the time you hit the legal limit. If you happen to drive drunk and get stopped, you will likely be arrested. From there, you will have to battle against the charges you are facing.
Source: B.R.A.D. 21, "Effects At Specific B.A.C. Levels," accessed May 03, 2017