Burning all organics off of live rock (and dissolving some of the rock) is one situation in our hobby where you may want to use muriatic (hydrochloric/HCl) acid. But for cleaning equipment/plumbing, which is how this thread started and what most would use it for, I stand by what I said that it has no place because the downsides outweigh any upsides.
Calcium carbonate and other biological buildup are very quickly softened and then dissolved by acetic acid and citric acid. After just 30-60 min even very dense buildup can start to be brushed periodically to reveal deeper layers and speed the process along if you are under a time constraint. If you do this, it is doubtful you would save any time using hydrochloric acid. Most of the time you shouldn’t be under a time constraint. If you are doing periodic maintenance, like you presumably are for anything that would be missed when it is out of service, then the whole cleaning only takes 30-60 min total. It never needs to take all day.
HCl is much more likely to damage equipment than the other options, and requires significant safety precautions that most people learning about on here won’t know about and many people don’t follow even if they do know about.
It’s not that I’m scared of or otherwise opposed to HCl, I use it frequently for my pool. I also don’t think we always have to avoid anything a little dangerous if it is important. I just think it is the wrong tool for this job for multiple reasons. Plus folks who are learning about the hobby by reading this forum would be much better served by pointing them in the right directions from the start, rather than in a questionable direction, just because it is possible.