If you're on your own in an R44 and try raising the collective whilst the blades are turning you're at serious risk of dynamic rollover, even if the rotor RPM is well below normal operating range.
Is the risk of a dynamic rollover less likely if you have others with you in an R44 when you raise the collective after shutting down? Please enlighten us.
The main reason I see adding a little collective as being a bad idea is the risk of ground resonance
If you're going to get into ground resonance, it will have already happened a long time before you shut down.