For sure you know whats happening, there are infrequent times when you've been tumbled and surrounded by a cloud of bubbles (sometimes they don't go straight up) when the alarm really does let you know what's happening.
Extreme currents can be a sensory overload, the more experience you have the more bandwidth you have to manage the situation but an alarm can be a useful conformation, OR as with me a number of years ago on a dive (in hindsight) well above my experience and abilities at teh time, an up current caused me to freeze like a rabbit in the headlights - it was the incessant bleeping which prodded me into action.
Occasionally I hear the alarms of other divers in our group ahead of me (no one else dives our sites) their alarms instinctively causes me to prepare and dump some air because there's an upwelling ahead (if I'm there first they get the same warning)
For more normal divers on vacation making a 30m dive on air, and being unknowingly narced that alarm might drill into their conscious that they need to take action.
That said. Mostly I'm on a DPV, and in current, on a pinnacle you follow the topography to "punch through" which means you'll be going vertically up a ridge wall, inverting over the top and back down again. At this point my computer is being annoying and I often tell it to shut up through my reg. Do I need my alarms on 99% of my dive? No. But its that 1% where they're useful
With regards to teaching, on AoW & above courses I ensure my student wear a computer with alarms on. I expect them to make the dive, carry out a free ascent (even if it's alongside teh anchor line - no touching) and launch a dsmb at or before the stop and hold a stop all without triggering the alarm.
That test bursts a few ego bubbles too, I wonder how many of the naysayers on here can do the same?
