The mortar bonds way better without drying out too fast.
Honestly, after seeing how a damp brush keeps the mortar looking clean, I switched and my finish work improved a ton.
A guy down my street decided to replace his old mailbox with a brick one over the weekend. He must have mixed the mortar too wet, because the whole thing lists to one side pretty badly. Now every time the mail truck comes, the driver gives it a wide berth. We're all placing friendly bets on how long until it tips over.