An AI computer will give you more than just a digital pressure gauge. It is constantly calculating on the fly how long your tank will last at your present depth, based on your actual air consumption.
Plus it has some features you can program concerning your air consumption. For example, you can set a "turn pressure". Lets suppose you are doing a shore dive out, and you want to start heading back when you get to 1250psi... just set the alarm for that and it will beep at you. And let's suppose you want to hit the surface with 400 psi in the tank. You program in that, and then you can also set an "end of dive time" of say 2 minutes. Then when, based on your air consumption, the computer will beep at you when you have 2 minutes to go before you have to start your ascent if you still want to hit the surface with 400...
Also the AI is smaller by far than a standard gauge setup... so that's nice as well.