The current trend in game design from Wizards seems to lean towards a balanced, fun-for-everyone, GMing is easy sort of thing. So encounters are intended to scale with your PCs. Is this actually fun?
Sure you'll get some tough fights, but for the most part, you know that your PCs will win unless they roll shitty or do something stupid. Sure, some of this tags back to "I don't want to kill a PC."
Most of the D&D games I've been have ended with TPK. It sucks.
But sometimes real heroes run away. And the real world isn't balanced in our favor. Real world challenges don't scale to our age/experience. Nor should they for a PC, or a party. I feel like adding real threat, an insurmountable foe, can add necessary pathos.
The villain who can't be fought, because his army is too large, he is unreachable. He taunts the characters, hovering just out of reach. They have to plan his downfall, arrange it neatly, think carefully. The players have to be clever. Or at least a facsimile of it.
These are my random gaming thoughts of the day.