The AI will cast Shelter after combat for no reason (picking a random color), for 0 benefit other than drawing a card. Then it will chump block with the creature on the players turn. If it had it available it's creature would've lived and it would've drawn the card. It also picked to play it over 2 Blessed Wine, which are truly just card draw. This is the sort of thing that happens with cantrips (I'm using shelter because there are so few in the pool).

As for better individual timing of the Shelter effect - outside of combat only if:

- it would make a creature survive being targeted by something else
- take an enchantment off a creature
- make the creature unblockable (so before combat)

Or in combat to make the creature survive it.