I sang in choirs from an early age, but (except for descants) sang the melody line until I was about 14. At that point a wise choirmaster insisted on a change to the alto line as a precursor to the voice breaking experience. Since then I've sung both Bass (well Baritone really) and (usually first) Tenor. What I'm getting around to is that most men who sing chorally, would have probably sung at least one other part. I often notice that many (I didn't say all) ladies who have always sung the Soprano line, have problems singing "middle" parts. I find that in harmony sessions it's usually the Contraltos and Mezos among the ladies who produce the most interesting harmonies - rather than just the equivalent of descants.

Devising harmonies (intuitively) is great fun - although in some sessions it's a bit like trying to avoid someone walking along the road towards you - you know the time when you move to your right and they move to their left... - sometimes it's best to stay on your first choice and let the other person move. I can always remember Dave and Annie saying that in "Beggar's Velvet", Charlie Yarwood always grabbed all the best harmonies first.
Finally, nobody has mentioned one of my favourite harmony groups yet "English Tapestry". I did open a thread asking for news of Brian & Ruth recently, but didn't get any satisfactory replies. Their harmonies were scored, but they probably needed to be, because they changed their third member (Tenor) several times. Probably the nearest to them nowadays is "Artisan", but "English Tapestry" sang a higher percentage of tradition material. Besides their skill with harmonies, they did some wondeful things with unusual time signatures and syncopation.