The old Mytton and Rheem kegs use 1/2" posts. The old ones have mushroom seals in the poppets. For me, it would be a lot easier if i could service them with standard poppet orings etc.
Someone already mentioned that the original 1/2" posts are getting harder to find, not that they need replacing that often.
I'm sure they could come in handy elsewhere in the brewery as most connections are 1/2". Would be handy to be able to put a ball lock post on something if the need arose. Keg line washing set up, possibly?