Positive loyalty taps a creature, negative loyalty draws cards based on the number of tapped creatures an opponent controls (hello, mass tappers), and the emblem turns your maximum hand size infinite and (optionally) returns anything that hits your graveyard to your hand
So if you have five extra mana hanging around after your first main phase, and you move to combat, you'll be taking five damage
A high number of Gitaxian Probe decks are more linear than this deck and just want to use Gitaxian Probe to make sure the coast is clear so-to-speak, but understanding the best time to pull the trigger (or not) takes a strong understanding of Legacy and your role in a matchup

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It doesn't trigger if you put Geological Appraiser onto the battlefield without casting it.