That must have been an interesting presentation!
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I would like to point out a basic reasoning.
What can be done and what should be done with 3D CAD is tied to its 3d engine and the stability of calculations.
while feature patterning (or mirroring which is a variation of it) is advisable to use it ONLY for cuts and holes. (no body geometry involved)
all the rest should be used as a BODY pattern or a BODY pattern and BOOLEAN operations in case of complex geometry.
This comes down to a calculation stability issue, and we had some “bug” with missing geometry here and there, because of the operator expected outcome looking at the feature list and the cad intricate calculation to avoid an ambiguous outcome, with some parent child feature relations in the middle to complicate things.
A body is the result of multiple features and it is never ambiguous, but multiple features could generate multiple bodies and during a pattern the cad will be mislead into a wrong outcome, at least from the operator POV.
As my 3d mentor used to told me: " 3D cad is always right and you have to cope with it"
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I think the SPR list, release after release, may put some doubt on that claim. 
It’s a very ‘sarcastic’ remark, in the sense that well even if it’s wrong, you’re the one that’s causing the issue in their perspective.
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“The problem is always between the PC screen and the chair”
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are you taking about the ID ten T errors?
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I believe he was referring to PEBKAC error.
While I agree with the sarcastic angle of the comment there is certainly an aspect of using the right tool for the job and using that tool correctly. Just because the user wants the model to work a certain way doesn’t mean they are correct. I’ve been there A LOT; life is easier if I align my modeling methods with the strengths of the tool I’m given instead of insisting to make my way work.
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You all lost your sense of humor today? No one see the winky face?
PS. Its just a tool. There are plenty of ways to use a hammer the “wrong” way… but at the end of the day if a nail needs to be smashed in… you aren’t going to give a flying fk how “right” you achieve it when you’re sweating balls in the hot sun in the middle of no where and a damn nail needs to be smacked in when there’s no room.. a beam/wall/tree/object is in the way so you can’t do it the “right” way.
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This is why I tend to not use mirrors. I have been bit by the errors created on mirrors to many times that I usually will just do a separate feature rather than mirror. If your going to be editing a part or changing things mirrors suck.
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I don’t know that I had one to start with, sarcasm goes over my head most of the time. I thought you had something in your eye. 
I think you’re spot on with working in the confines of what you’re given. I like your analogy and have certainly done plenty of side hammering, sketchy crap. Sometimes the unfavorable situation changes the definition of “right way”. When it’s tough going we just dig in, put our head down and keep hammering come hell or high water. I’m slowly learning (mostly as I get older, things hurt longer and a few too many near heat stroke events) that it might go better and even more quickly if I pick my head up, look around, reassess and try from a different angle. Maybe a couple screws driven by a right angle drill where there’s no room to swing a hammer for example. That’s all I’m saying.
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Mirrored bodies or features?
Bodies are somewhat better at being mirrored without issue, but I still usually tend to avoid them. I also don’t do many multi body parts outside of weldments.
The entire multi-body doesn’t make a lot of sense to me because of part numbering and other file tracking issues associated with it.
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I agree that many people who have problems with mirroring in Parts would have better luck if they mirrored bodies instead of features. Also, I have often seen long-time users recommend people stay away from mirroring in sketches, but I have had good results with it, and do it often.
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For me, its like most things in sketches, as long as the gemetry is fairly simple, I use sketch mirrors. It’s the Autocad users who insist on sketching the entire front view of the finished part and fully define it that drives me crazy.
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… and calling patterns “arrays”…
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Pfft…programmers 
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And then there is array and array classic to choose from
Autodesk is too afraid to let the old command die. Just make the new one do everything instead of maintaining an old function and bloating the software further.
that is not bad, and the correct way to handle a software improvement.
Just compare it to SW that changes legacy commands with unwanted defaults or break their backwards compatibility…
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Dumb 2d and parametric 3d work a bit different. Most geometry in ACAD is dumb, so changing the way a feature works doesn’t usually affect existing geometry. So leaving “Two ways” to create Arrays is just extra maintenance that isn’t needed.
3D parametric features have it a bit harder as each “feature” is a mini program that rebuilds over and over during the life a part’s history. So changes to the “fillet” program need to maintain some backwards capability and integrity. Something SolidWorks has not always been successful with.
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