BryanG Has the right idea IMHO. As this is NOT a semiconductor circuit any discussion of semiconductor sink/source discussion is mute.
The problem I saw:
1) Very uncommon method - ie. Not a best practice. Unexpected operations or methods are the #1 source of hazards/ No clear advantage to stray from best practice.
As stated by BryanG:
2) Hazard of actuation of the device in the case of short circuit on the return 24VDC common (NOT ground or earth).
I also note that in a perfectly isolated DC power supply system, grounding or earthing either the supply or common should result in no current flow. However due to additions and poor wiring practices, devices connected that mixed their power suppplies with the system power supply, breakdown in isolation insulation or improper grounding, this can be compromised and result in current flow to earth.
Now BryanG also asked which side of my 24VDC is grounded. Which brings up the discussion of grounding DC control power supplies. If you ground the DC power supply, then common is no longer common. If you have local code regulations that state this is necessary, please reveal that. As this is low voltage, I doubt there is any code to follow so then it becomes a design/methodology discussion. How many people ground their DC control power supplies and why would you do that?
Thanks for all your feedback people. Anyone in disagreement?