Which advantages does it have to use an RTK drone (e.g. a Phantom4 RTK)?

RTK is a technology to calculate a centimeter accurate position using GNSS signals and corrections fron a basestation. Because the position off the drone-photos is more accurate, also the absolute accuracy of the result will be much better. (Typically <5cm without ground control points)

With a Phantom4 RTK you can also create better 3D models of facades, because you can fly at multiple altitudes to take images.

The data recorded with a Phantom4 RTK also processes much faster in the AiroCollect software, which is much more interesting for large areas or if you fly a lot.

Via a mobile data connection your drone can receive RTK corrections from providers like FLEPOS (Flanders), Walcors (Wallonia), 06-GPS (NL)…