20H rule EMI/EMC effectiveness
In my experience, it doesn't make a lot of difference.

The advantage: the local electric (near) field at the edge of the PCB is somewhat reduced, useful to minimise cross-card interference (which is why I use it where there are a number of cards in close proximity). Because the near field is rather chaotic, all types of coupling are potentially there, so reducing this can be very useful.

Total radiated energy in the radiated field is slightly increased.

The resonant frequency of the PCB is raised slightly with pullback.

Details in this research paper

My methods for keeping emissions down are the usual management of signals that could be problematic, and careful shaping of the planes (not the edges, but making currents flow where I want, not where they would go otherwise).

You may find this answer useful.