and what if I already have channels programmed that I want to listen to if I am in the area will they automatically comeback on
If you program favorites lists in the Uniden GPS enabled scanners, you have the option, in the computer software, to enable or disable location control. If you have the location control disabled, which you probably would if you entered the frequencies yourself, without adding in the lat/long and range of the transmitters, your scanner will scan this favorites list regardless of the GPS status or location if you have it turned on to scan. In other words, it will always be on.
If you create the favorites list by copying and pasting systems, departments, and channels from the master database, then you will have the option to enable the location control, which will turn the list contents on and off via GPS, or leave it disabled to scan it regardless of your location.
The only major issue I have had with using the master database and GPS while traveling is when I come through an area which has transitioned to a MOTOTRBO or other unsupported digital system the scanner is unable to decode. The scanner will then stop on those channels and emit a horrendous noise, sending me to the AVOID button to hit it twice to permanently lock out the frequency. Unfortunately, the database doesnt differentiate from one digital type to another, so there is no way to tell it not to stop on those frequencies it cant decode.
If you drive the same routes, areas...then once they are locked out, they will stay locked out (if you hit avoid twice when it stops on one), but if you reload the database, it clears the avoids, and you have to do it all over again the next trip. That is the only downfall to the GPS system I have found so far.