Do you need to remove that standing water from the pan, or should the service tech have done it? Strictly speaking, the answer is 'no' to both, but neither is a bad idea. Yes the water would eventually evaporate out of that catch pan but you're right that this could take a while. It would have been a sign of thoroughness for the tech to have removed the water. At this point in the season it may be that he has such a long list of service calls to complete that there's no time for doing anything that's optional.
International Residential Code (which I'm assuming would be applicable to your location in Georgia, USA) makes some requirements about condensate drains. See IRC 2015 M1411.3.
Part M1411.3.1 requires secondary protection where damage to building components would occur as a result of overflow of the primary condensate collection system. This stuff is normally applicable for an air conditioner located in an attic. The Code offers the choice of four options:
- auxiliary drain pan with separate drain
- secondary drain line attached to the equipment built-in drain pan
- auxiliary drain pan without a drain, but with a water level detection that can shut down the equipment prior to overflow
- water level detection that will shut down the equipment if the primary drain is blocked
It sounds like your system is installed as a hybrid between the third and fourth options.
That said, water damage is a big deal and a belt-and-suspenders approach to prevention is prudent. While the water sensor saved the day this time, you might consider it worthwhile to revamp things so that the secondary drain pan actually does drain away rather than merely holding water.