It'll be a boost gauge.... but even if your eventually going to mod (and even not), it will help you understand and predict your car more.
In the speed line (3,6, and CX7), the behaviour of the vehicle is so dependant on the MAP temperature. Have you ever driven your car sometimes and wonder why it's slower than a civic (exagerated)??
When the temps get over a certain degree, a few things happen.
Boost lowers (as high as 3-4 psi depending on temp), timing gets pulled, plus the hot air doesn't burn as efficiently with the gas = slow. Plus you'll know you shouldn't be mashing your gas pedal, cause it ain't so good for your turbo.....
After experience... when your BAT temps are....
80-95 - Fast, you'll log your top boost numbers
96-105 - OK to mash pedal, and car still pretty fast
106-115 - You'll notice a little power loss, and less boost (could even start knocking)
115-130 - Wouldn't mash the pedal
140+ - Don't even dare line up with a Civic....