Ideally, anytime you increase boost, it's a good idea to have the car retuned to the new boost levels, especially to ensure optimal running conditions. If the computer is not tuned to deal with the new boost pressure, it still tries to compensate, but not as ideal as if you have a tuner adjust it optimally under load for the new conditions. Many people put a new pulley on the ZL1 and make a lot more power, and never touched the tune, but it's not as optimal as actually tuning for the new conditions. Obviously, with a turbocharger, boost is not increased through a pulley because it's not belt driven so to speak. So, back to the turbocharger and AEM Tru-Boost....to take full advantage of the controller, you would really have multiple tunes made for you at various boost levels you want to run, as well as how you want the car to run in certain situations like 1/4 mile, autocross, street driving, etc. So, you would have tunes saved on a handheld programmer, upload it to the cars computer via OBDII port, and adjust the turbo controller to the boost level that correlated to that tune. The Tru-Boost doesn't have a feature where you just toggle through buttons selecting "Boost- 8psi", or anything like that unfortunately. The boost is increased or decreased by "Duty Cycle" on the gauge, which your tuner will use while tuning. AEM explains Duty Cycle as simply a comparison of the devices on time versus its off time. For example, a duty cycle of 50% inputted on the device means the device is on half the time, and off half the time. A duty cycle of 10% means the device is on 10% of the time, and off 90% of the time. The Tru-Boost solenoid is pulsed to control the pressure going to the wastegate. A higher duty cycle means an increase in boost pressure.
So, with that said, having multiple tunes for various situations and adjusting boost on the gauge gets damn expensive because you'll pay for each new tune, and is usually too much work for most people unless they race a ton. I purchased the AEM Tru-Boost controller because I simply wanted to increase boost electronically without having to change out the wastegate springs to a higher spring pressure (even though this is the most reliable way). Your boost would be what spring pressure are in your wastegates currently, and then the boost controller increases additional boost from there with it's duty cycle operation electronically. I simply have no need to change boost pressure all the time, LOL. Just tune the car to a safe, yet fun boost level, and keep it there regardless. Then, adjust your driving habits from there.
Also, don't skimp on your fuel system. Either go with Dual fuel pumps or the ZL1 pump with ADM's alteration, as well as large enough GOOD injectors to hold up to the power you demand without overstressing them (like Injector Dynamics, who actually has the data to input while tuning. That's huge right there for optimal functionality). If you plan to not increase the injector size and/or the fuel pump(s), be very careful how much you increase boost. You'll be playing with fire, and when something breaks, so will your heart and your wallet.