Presumably they'll charge you a fee to buy, sell and trade it just like any other asset. If coinbase is involved in keeping the reserve, they can invest it various assets and keep the earnings - think money market fund, but you don't earn any interest - coinbase/circle keep the interest.
> If coinbase is involved in keeping the reserve, they can invest it various assets and keep the earnings
If that's the case I wish they were up front about that fact. I think its completely reasonable that they would keep any earned interest as compensation for managing the coin, so just be honest about it.