The main difference is in the amount of money they'll be holding for that time. The 24h volume now shows XMR 24212. If a transaction takes 10 minutes (let's take the average Bitcoin confirmation time for this), it means they hold on average XMR 168 (or the Bitcoin equivalent) of their customer's money. If you add a 12 hour waiting list, this amount very quickly goes up a lot.
True, but that's statistics. It's a matter of trust to send them your coins now and it becomes a matter of more trust to allow them to hold your coins for a definite period. That's how I see it.
If there are no reserves for the coin I want, the exchange has to send back my deposit. I then have to deposit a second or third time if I am unlucky. That's throwing away money on fees.
That's a good point.
And both sides are losing here, I think. Every time I send coins to the exchange only to have them returned, I lose in fees. I am assuming the exchange does as well for the return transactions, or do they take a piece of the original deposit to cover the mining fees?
If it was optional, I'm not sure how they would manage it. The moment XMR comes in, where will it be enabled first? On the regular exchange or the orders on the list will have priority?
You wouldn't be on a waiting list if they had the coin you wanted in their reserve. It should be on a first come first served basis like it is now. If my deposit confirmed before yours, I believe I should have priority over you regardless if I ticked the waiting list option or not.
If there are no reserves for the coin I want, the exchange has to send back my deposit. I then have to deposit a second or third time if I am unlucky. That's throwing away money on fees.
The same thing could happen if you are on the waiting list for too long and you want to give up and withdraw your funds.
True, but the odds are more in my favor if I choose to wait. It's more than likely that someone will come and deposit the amount I am looking for in the next x hours. That's what's happening every day.