Among them are a holding pen for plot-critical NPCs to hang out in, and a "magical teleporting death journal" to point you in the direction of Act 2 should ... because BG3 uses the same NPC ...
Is it worth pursuing the Necromancy of Thay questline in BG3? Absolutely. While the final bonuses in Act 3 are the real highlight, getting to interact and even fight some memorable characters ...