Precise GNSS positioning needs a baseline to be measured.
You have to fix two receivers in place in order to define a 3D vector.
RTK mode is extremely fast, even if less accurate than Static mode.
You need two antennas: a fixed base and a mobile rover.
It is not the cheapest solution (you need two devices) but it does have some advantages.
If you are used to working with an nRTK receiver via GPRS connection with fixed bases (from which you receive corrections in real time), you know that if you’re gonna work in an area without GSM coverage you may be in trouble.
RTK base-rover could fix it!
If you need to be super fast and you have to measure the coordinates of many points in a short time, this method allows you to avoid waiting times for GPRS connection and receiving corrections.
If you don’t need extreme accuracy you will definetly go faster.
Base and Rover talk to each other via radio that, over limited distances, it is more stable and solid than telephone network.
Moreover, in this way you can even reach 1 cm of planimetric position, against the 2/3 cm of a single nRTK receiver.
Unfortunately you must have a second receiver available.
And that’s not cheap of coure.
But you can always rent it!