Most people think its for looks and asthetics but it does provide a usefull function. If you constantly boosting at 25lbs for example and then you start dropping 1 lb regularly...you have a leak or worse. Its a good way to guage the health of your entire system. Dodge should have included one in the darts but because its more so a 'performance' guage on a performance car type of instrument (which i disagree with personally) they didnt. Knowing your levels at all times can help you solve issues, or prevent severe issues from happening due to lower levels.
These are classed as 'economy cars' which is why they were never included in the different trim levels, but for drivers knowing whats going on with their car and who care we are left to fend for ourselves and mod.