Do you use electric clothes dryers?

BooJewels

I must admit @Bendy_House - if I'd been asked to guess beforehand, I would have expected less water in the garment at all - the 86ml seems a lot for one small sleeveless t-shirt - it added 37.5% to the weight!   No wonder my machine knocks when full of wet towels.

I might have guessed, of what there was, that a greater proportion would have spun out and less would have air dried - nearer a 50/50 type split - not 19% / 81% - and that something that only feels damp still contained so much water.  I'm also surprised that each subsequent spin still got some out - albeit in diminishing amounts. 

Was it worth it, yes for a couple of extra spins - for me - I doubt I would bother with more - and definitely when only a penny or so more cost.  If nothing else, dropping some of the weigh out of bulky items like a king size duvet cover is helpful to me if I have to man-handle it over the rack, which when lowered is still at chest height for me - on account of me being very diddy.  And if ten minutes extra in the machine drops 2 hours off the drying time, then still worth it. 

The financial benefit would perhaps come for tumble dryer users - that 12ml of water per item in a wash (i.e. after 2 additional spins) is likely to cost a lot more that tuppence to remove using heat.  10 items in a load would be potentially 120ml of additional water to dry out.

I'm not surprised by your bus shelter library findings - it's air movement that facilitates drying.  We did a lesson on this, several decades ago in domestic science at school and had a list of weather conditions in order of efficiency for line drying laundry and I always remembered that cool moving air is more efficient than warm still air.  Warm moving air being the optimal - your 'good drying day' - warm, sunny and breezy.  As mentioned, I find my rack so efficient for me, that it has to be an exceptional drying day for me to prefer line drying to my rack.  I don't think I've pegged out washing all summer.