I have never been good at what singers call 'marking'. I would never attempt to sing my way through a rehearsal in 'half voice', as my current theory is that doing that badly would tire my voice out much more than singing properly at (almost) full pelt. As for 'popping it down an octave', well, I can see some sense in that, however only with music that I know is absolutely dialled into my voice and body. At this stage in a singer's career this is hardly ever the case, as most of what I perform is repertoire new to me, and even if it's revisiting roles or pieces I've done before, my voice and technique change so rapidly that it is often a case of relearning to sing old pieces with a new voice. Maybe I'm too hung up on 'singing it in' and have a tendency to overwork my voice? Then again I never practice hard passages to self-destruction, sing scales until I crack or warm-up to within an inch of losing my voice (common 'rookie errors' among young singers). I also learn music silently or falsetto, working out a game plan for singing it before properly opening my mouth. The 'singing in' and practice come when I'm sure I know what I'm doing and the aim of the game is to cement consistency. Once I have consistency, why risk unbalancing it by trying to mark my way through?
I may be wrong, and even if I'm not, this is probably an approach that won't work for everyone. Tiredness happens, especially when like this week, we have to sing a lot and want to give it a 100% because we're working with a visiting tutor and want to make the most of it. Singing when I'm tired makes me all the more focused and pushing myself is what stretches my stamina. Of course, if I felt I was in danger of hurting myself, I'd just stop singing or do the 'octave down' thing, but as a last resort rather than default practice.
I say all this, but probably only because I can look forward to a weekend of silence, so please disregard the above and treat it as a snapshot of my thoughts after this week only. Perhaps next time I'm in a long production period I will turn to marking and report on here for comparison.
Disclaimer: The author is not a singing teacher or established professional, but in fact just a student and probably has no idea what he's talking about, so don't try this at home!