Milling random cards will give pseudo card quality or card advantage, or it can be a mana saving too
It also means your opponents basically can't block you, and abilities from opposing creatures can't target yours
If you cast it without a Time Vault, you could go find it and threaten to take infinite turns, next turn
Counters Many of these payoffs are in blue specifically, like Lyla, Holographic Assistant and Teferi, Temporal Pilgrim, but of course the Simic flag bearer for this effect is Lorescale Coatl
Things appear more stark over at TCGPlayer where, for instance, Tropical Island costs $335 if you want a Revised copy from 1994, but $999 if you want a retro frame 30th Anniversary edition from 2022
Its primary strategy revolves around generating Eldrazi Spawn tokens and ramping mana to summon massive Eldrazi creatures that can dominate the battlefield