My experience

I've been to higher altitudes many times but have only used it a few times. The latest was just last week. Since I have had severe food poisioning from the Houston Airport for three days I missed all our acclimatization climbs except for one, so I took Diamox before climbing Cotopaxi as a preventative measure.

Personally I don't like the side effects. It makes you tingle as if your hands or feet are asleep and also makes you pee a lot. Sicne I already have a small bladder that side effect is not pleasant.

If you don't have to use it, I wouldn't, but I would always take some along. It is both a preventative and a treatment just in case. It should never be used to ascend to a higher altitude if you already have AMS.