How does defeating every Minecraft boss affect the game?

The Wither

• 50 experience
• 1 nether star
  • Can be used to craft a beacon with 5 glass and 3 obsidian
    • Can provide speed, haste, resistance, jump boost, strength, and/or regeneration to players nearby

The Ender Dragon

• 12,000 experience if it was the first time you killed it, otherwise 500 experience.
• If you killed it for the first time, a dragon egg generates above the exit portal.
  • The rarest item in the game as you can only legitimately gain 1 per world
• The exit portal (the bedrock structure in the centre) activates
  • Allows you to return to the Overworld
• An end gateway generates floating within 75–100 blocks of the exit portal (up to 20 times)
  • Enables you to access the outer islands
    • End cities and end ships
      • Loot
      • 1 elytra, which can be used to fly
      • 1 dragon head
    • Chorus trees
      • Chorus fruit
        • Can be eaten
          • Restores 4 (2 drumsticks) hunger
          • Get teleported to a random location within 8 blocks on all axes
        • Can be smelted into popped chorus fruit
          • Can be crafted into end rods with 1 blaze rod, which provide a light level of 14
          • Can be crafted into pupur blocks, which can be crafted into pillars, slabs, and stairs