They sell them at the Window Clean Centre and the Window Cleaning Warehouse.
I haven't used one for a while but they are very absorbent and can be wrung out and used all day, unlike other cloths. I would use one with another cloth, though. Chamois first, to get rid of most of the water/moisture and then polish/dry with a scrim/micro.
If you were to use for detailing, use it to pre-detail and then use a scrim/micro to finish off.
They would come into their own in the cold, damp months, when you could use it all day- keep wringing it out- and use fewer drying cloths.
The price of scrim and m/fibres has come down a lot, recently, so people would tend to use more of these. But if you can't be bothered to carry loads or don't want to keep washing them, the chamois is very good at absorbing moisture befroe a final wipe.