The general rule of thumb is that you should exhaust your cards at the last possible moment.... There are plenty of treachery cards that hit "tapped" cards. Being tapped is a card state that things can trigger off... being untapped is as well though. Still look though the decks and you should see a lot of bad stuff cards that will effect only tapped cards.
Denathor. If you tap him at the start of the quest phase.. you can scry.. that is all good.. but now he is tapped and effected by those treacheries until next turn. OR you can tap him just before the refresh phase. This means you can scry the deck twice in a row is needed, once before refresh and again after refresh. You also have him ready to scry the shadow cards as well if you want.
Daughters of incomprehensible fantasy name can heal your heroes. Though these are actions and there is a action window after shadow card reveals. So in general it is good practise to only tap her at this moment, as you leave her ability "up". I mean there is no point in tapping her to heal 1 dmg off a hero, then seeing a +3 atk power shadow card. Best to heal 2 points off that, and then untap at end of turn and be ready for next turn. Juts remember that during the quest phase there is NO action step between the reveal of each encounter card. So you can not user her heal to make a hero survive a treachery.
As for your Ziggy example.. again.. If you do it at the end of phase you have many more options. You cna do it twice in a row for a massive resource boost, you have Gildor ready for quest/def/attack is needed, you are immune to treachers that affect tapped cards... etc etc etc
So in heneral I think the rule of thumb should be to only tap a card at the very last possible moment.
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