It's common to have a common ground. After all - unless you make the sections totally isolated from each others (transformers, optocouplers etc), there need to be a potential reference between them or you will not be able to send electrical signal between them.

The issue here is more if all parts of the design should be a single huge ground plane on a PCB, or if there should be cutouts in the PCB to reduce the amount of noise between power electronics, digital electronics and analog electronics. Still a common ground, but with filtering at critical locations.