Boss battles are usually the culmination of something, whether it be the end of a dungeon or the end of a campaign. They cap things off, and test the party on everything they’ve learned so far. It’s no wonder DMs want to get it right.
All tagged combat balance
World Weaver's Guide to Combat Balance: The Basics
Combat balance in D&D is one of the toughest skills to grapple with, especially as a new DM. However, combat makes up the majority of the game’s core rulebook, and most character abilities lean into combat efficacy. Plus, making cool fights is just really, really fun.