I do think there's a benefit though: not being able to know how much currency is in circulation isn't a good thing when you're relying on the rest of it to raise in value. There's no need to return the coins to circulation, but voiding them after some time has advantages - it would let you know how large the money supply is, and it would allow old blockchain history to be dropped completely after the coins expire. (The current pruning scheme often can't remove old blocks when some outputs are still unspent.)
The only reason anyone cares about how much is out there is because they are trying to manipulate the economy. The free market doesn't need to know the total amount of currency, and neither do the individual participants. They only need to know how much stuff they can trade the money they're holding for.
Its the politicians that care about things like M2 because it gives them a big knob they can turn to "fix" the economy. The big open secret is that for politicians, doing something - even if it is actually the wrong thing - is better for their career than doing nothing - even when that's exactly what they should do.
