Dead and false sole can usually go. (There are exceptions) It needs to go so you can determine the actual sole plane and trim to it. Live waxy sole should be left alone. Leaving dead and false sole can cause bruising.
Hmm, now I agree that if you don't otherwise have a good idea of where the *live* sole is likely to be & balance in this regard, removing dead sole can be helpful. I also agree that leaving too much dead sole can potentially(rarely seen this, more usually the opposite IME) cause bruising, as with overgrown, laid over bars. I absolutely agree with not invading live sole plane, but I'd have to say that generally(there are exceptions), dead & false sole can stay unless it's obviously ready to come off & is usually best left, in order to *avoid* bruising, by leaving more 'armour' to protect the foot.
Also with regard to someone learning & not having clear ideas of boundaries, I'd say if in any doubt whatsoever, leave it.
(leave the heels about 1/8 inch higher than the live sole)
There are many reasons why leaving the heels a tad higher may be appropriate, but as a rule, I believe the entire hoof walls - including heels - should be balanced in relation to the sole plane. So if you trim the toe to level with the sole, that's where you should take the quarters & heels to as well. If you leave 1/8" extra wall at the heels, that's about how much longer they should be at the toe also.
Of course, these are basic principles & generalisations, not 'rules' to follow absolutely.
Wow, Trinity, I think this is the most I've ever differed from your opinion in a post by far!
This thing is, IME few domestic horses have this foot when you first start with them.
That is absolutely the crux of the issue IME too, that relatively few horses I see have truly well formed, functional feet, so you generally have to adapt & change at least some of those basic principles of trimming in order to address problems. This is a major reason why I don't think learning from books & vids is good enough for people generally - a basic trim is inadequate or inappropriate in so many situations, but then it's almost beyond the scope of books & vids to explain all the ifs buts & maybes.