Autoplay is great. Occasionally, it is terrible.
This sounds like one of those puzzles, but I discarded a Faithful Hound with an Inn the other day after having drawn my thin deck, planning to draw it back with a cantrip, and it got set aside; I needed it to trigger my Magic Lamp (maybe it was Leprechaun) and lost. (It's not a true gotcha in that I also could have discarded some other stuff, had I been smarter).
Any other autoplay problems? I've turned autoplay off for the travelers; making the decision matters too often.
I suspect it's healthiest to play with most of the autoplays off, except Crown, Changeling, and Coin of the Realm. The problem is that you don't realize "hey, this is one of those boards where I might not always reveal my Moat" until your opponent plays the attack you didn't want to reveal Moat to.