I am saying that if you need to use one specificaly to make weight for a fight, and that you have 24 hours post weigh in to rehydrate, then its a necessary evil.

For all other instances I would say dont use them. The whole 'wow look how hard i worked- look at all that sweat' is a psychological thing, and does not correlate with any physiological benefit.
Any weight you lose through accelerated dehydration you will regain through normal eating and drinking over the next 8-12 hours, so the extra risk from dehydrating yourself on purpose is a fruitless endeavour.
Don't let the door hit ya' where the good lord split ya'