Edwardthepilot:

"The best way to do a controlled descent without oscillations in the CRJ is to use the VS mode. The only place and reason I would use SPD mode (or rather descent mode) would be when getting told to reduce and keep a speed inside a TMA while descending. Initially I would set VS to get the descent rate I wanted, adjust the thrust levers to the speed I was told to keep. Then I would when these two where met hit and engage the Descent Speed Mode and just do minor corrections as we get further down to adjust my rate of descent slightly. 

The CRJ will irl oscillate ALOT if you try starting descent from cruise down to landing with SPD mode. This naturally as your IAS vs pitch vs VS changes with a number of factors as you descend from high up in the atmosphere down towards ground. That is why SPD mode most likely is not mentioned. I have never seen anyone out on the line use it apart from in the scenario I mentioned above. "

VRefSimmer:

"Here is one other great use of SPD mode in the CRJ:

If you have a depressurization in-flight and need to start an emergency descent down to 10,000' or the Minimium Off Route Altitude in mountainous terrain, after initially selecting in a lower altitude, pressing SPD mode for the descent with the thrust levers at IDLE and the flight spoilers deployed will ensure that you get maximum descent to the lower altitude without an increase in airspeed (per the checklist you will later be working through). SPD mode is great for allowing the crew to spend more time focusing on checklists and communications in this situation."