Progress After the First Major Battle
With the first few bosses defeated, the world opens up. New items, dimensions, and crafting systems become available. Players can now access mid-tier technology mods and enchantments that accelerate progress. Some really important items crafted from boss drops being, the Magic Mirror, Charged Ender Pearl, and Preserved Flesh.
At this point, you have enough to properly begin exploring the Prisoner's Quarters and upgrading your armor and accessories. Being able to take on stronger mobs and farm for rarer drops as you being to level your skill tree and gain new spells and weapons, before taking on the dangerous Prisoner's Quarters, and beyond it the Promenade.
The Post-Boss phase allows for experimentation and creativity. It's a time to reinforce your builds, optimize resource flow, and prepare for the dangers that await beyond the Overworld. With your new access to the Prison, you gain new materials and weapons to upgrade your equipment with.