Warm up before oil change?

I guess everyone has an opinion on this, but Rotax says you should.  I’ve done it both ways and I feel like you get a bit more oil out if you warm it up first. And regarding air in the supply line, I would think it’s just the opposite and running the engine until warm would purge any small amount of air in the line. Maybe he meant that once the oil is warm it would tend to drain out of the supply line easier during the oil change???

From the 912iS line maintenance manual:

NOTE
Run engine to warm oil before beginning oil change procedure. To change the oil
the following steps are necessary.

I think the amount extra oil you get out is inconsequential.  However, since you're going to have to turn the prop to accumulate oil into the oil tank in either method, warming the engine may help suspend gunk that has congealed.  So, in theory, by warming the engine you'll get more junk out.  Of course, that's what a filter's for.  But why not?  Of course, the manual calling for it seals the deal in my mind. 

The Rotax Line Maintenance Manual Section 12-20-00, Page 46, states the following:

OIL CHANGE:

NOTE: Run engine to warm oil before beginning oil change procedure. To change the oil the following steps are necessary:

We also have a video on Rotax-Owner.Com that shows the oil change procedure here: https://www.rotax-owner.com/en/videos-topmenu/expanded-video-instructions/39-exp-si-27-010

Therefore, whoever told you that you did not have to run the engine before an oil change is not following the proper procedures in the Rotax manuals.

Okay I want to look at the scientific side. Curiosity: I know killed the cat. 

What is gained by warming the engine first?

The only thing I can see is a little better flushing, but at what oil temp does it have to be to get that better flush? The warm oil will run out a little faster than cold oil which may help flush some of the thicker particles in the bottom of the oil tank.

Rotax-Owner, Do you see or know of any other benefits with warmer oil?

I think the warm oil helps flush out clumpy or thick (lead) deposits MUCH better than we realize. I can see this effect when I pour the used oil out of my drain pan into a container. The thicker stuff flows out much better if I don't let it cool off too much.