PPK uses exactly the same processing method as RTK, except rather than process in real-time it just logs the information and the merges with afterwards with the data logged from a base station. This is used primarily for remote sensing applications where centimeter accuracy of data is only needed in postprocessing and not at capture time - eg. drones with cameras for 3D reconstruction.

The reason to use PPK is weight and cost - it just uses a normal GPS receiver and doesn't need an RTK sideband antenna, since the base station information can be downloaded over the internet at postprocessing time.

RTK/PPK gives ~3cm precision, while standard GPS gives 6m precision. This new dual-band giving 30cm precision means it is good enough to not use RTK/PPK except in the most demanding applications.