"I have heard different opinions as to whether Obstacle Departure Procedures are required or not in IMC. Can you explain?" - Chris D.
“It’s important to understand the different types of Departure Procedures available to the IFR pilot.
There are two types of Departure Procedures – Obstacle Departure Procedures or ODPs and Standard Instrument Departures – the more common SID.
Obstacle Departure Procedures are pre-planned IFR procedures which provide obstruction clearance from the terminal area to the appropriate enroute structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure such as a SID or radar vector has been specifically assigned by ATC.
Standard Instrument Departures are ATC procedures for pilots and controllers to provide obstruction clearance and a transition from the terminal area to the appropriate enroute structure. SIDs are primarily designed for system enhancement and to reduce pilot/controller workload. ATC clearance must be received prior to flying a SID.
Although not required by regulation, (Part 91) pilots should fly the ODP at night, during marginal VFR or IMC conditions, whenever one is available.”