The one uber random use for relics and shards:
If you put it in your deck, clicking it uses the card but it doesn't make the card disappear/discard.
So if you spam click a relic/shard, you can reduce your quantum to 0.
If you have a rainbow deck, and you've played all the cards you need to, you could use this method for preventing from getting owned by black holes.
Otherwise relics are useless, and you should upgrade shards xD