Adventure balance is one of the terms that makes my teeth hurt. Not a fan. I understand the concept, but for my games, I don't like it in practice. Most of my players know I don't like to pull punches and not every situation they are going will be in their favor. I will add most of the time it's my players who jump into the deep end of the crap pool.
When I make adventures there are encounters that are going to be easier or very difficult for the players. In Knowledge Illuminates, a 1st level adventure, there is an encounter with an Ankheg that could be party killer. If the party tries to go toe-to-toe it won't end well. But if they choose to go after it, they'll need to come up with a plan. That's where the fun is. Also, in the same adventure, there is a very bad, bad magic item that could do bad,bad thing to the players. But at no time is anyone telling them they have to use it. There is a group that will tell them not to use it and there are enough hints that using it will be a bad, bad idea.
While I don't like to go out of my way to see that encounters are balanced for the party. I do playtest my adventures. I try to run them at least twice and if I can get some one else to run the adventure once. I want to see if I inadvertently created a death trap. While I am not into balancing encounters I also won't create unavoidable, mindless death traps. It's frustrating to the players and boring to me. When I playtest an adventure I can see where the problem are.
A good GM can also adjust the difficulty level of an adventure fairly easy. I can build an adventure for 1st thru 3rd level dudes. My parties usually consists of four guys. So that's what I write for. If your group has six to eight guys the encounter might be to easy. So while an adventure may have a suggestion of levels, it depends on size of the party. Some of them bring hirelings in tow. At this point the GM could increase the number of the enemies or increase the hit points or hit dice of the creatures. Or whatever way you chose to create.
I've had dragon or giants or liches in 1st level adventures. Usually they played an peripheral role, but if the PC wanted to challenge, suck up to, or, as one player wanted, to pee on the sleeping giant than rewards are given out for stupidity, cleverness or the distance of the urine stream. Most PCs are smart enough to avoid, or watch. But once in awhile a player is going to want to make a power play at a low level. If they can pull it off, bravo. If they don't, more likely they'll be rolling up a new guy.
In my experience, these unbalanced events/encounters are what my players find memorable. They can be built into an adventure arc the players are working through. Think of Conan and his parents and friend slaughtered by Thulsa Doom's men. It set up the first stage of an epic.