EDITED FOR CLARITY:
I realize that other posts have skirted this issue in the past, but I’m now at Dorico 4.1 and am not sure if the changes promised in past years have happened.
In a nutshell, adding measures or beats, regardless of how many parts or players are affected, screws up my score in multiple ways. E.g., I just copied 8 measures of music – in ten instruments – into the middle of a longer piece. Woops! I was careful to ensure that I added the same number of beats to every player. But it didn’t matter. Dynamics markings in later measures are scattered all over the place, embedded text no longer lines up, different types of barlines got mixed up, etc. Worst of all, the cues (or whatever they’re called – I can’t find a name in the manual, but I’m referring to the bookmark/notes managed by the bottom icon in the Notations toolbox) shifted by one position; that is, the third comment/cue/bookmark/whatever moved to the pre-insert location of the second one, the fourth moved to the position of the third, etc. – and no, their spacing is unrelated to the length of my inserted material.
All of this has rendered Insert Mode a choice of last resort for me. It’s much easier to do even simple insertions the hard way: count the measures to insert, insert that # of new blank measures, select the material to be copied, copy it, go back to the blank measures, and then paste.
If I make a subtle mistake and don’t select content of exactly the same duration for every player (easy to do when there are rests or ties across barlines) the problems can get so confusing that if I discover them later on, my only solution is to just delete entire blocks of content and replace it with an excerpt from an older version.
There was talk in an older thread about a feature that would let users ID an insert-mode endpoint, beyond which content would not be affected by a particular Insert operation. I can’t find any documentation on such a feature – did it ever happen?