I have a 38 mile round trip every day. Once the temperature is below freezing, unless I'm in the mood for an entirely unheated drive, I'll need to burn some gasoline.
My overriding rule is to try to keep to one warm-up cycle per day. I figure close to .1 gallon is being used just to get the engine block and plumbing warm enough to be useful for heat and there's no point paying that toll twice in the day.
If the morning temperature is below 15 F then I'm committed to burning gasoline anyhow, so I take steps to ensure that my return trip can be purely electric.
About the last 1/3 of my morning drive is freeway, so I kick in Hold until I'm within 3 or 4 miles of work, then use the residual heat to get there.
Why add Hold to ERDTT? Because if the day stays below 45 degrees my return trip is going to take more out of the battery (an extra 1.5 kW for the first 15 minutes) to bring the battery up to temperature after cold soaking at work all day (I can't plug in there).
Assuming no ERDTT in the morning, I just use whatever electric heat I need and leave the engine off until the afternoon drive.
For that cold afternoon drive, I have experimented with switching the ERDTT setting to cold to get my heat and range but have concluded that I'm better off kicking in Hold mode for the first part of that drive to get me the heat and battery for my return.
We also have a 2011 Prius and what you say above is absolutely correct, as it is for any ICE-driven car.
The big benefit of driving a post-2012 Volt is that I can manipulate things to reduce the number of warm-up cycles in a day.