I'm not sure anyone is suggesting that it is.
There are however many DMs who swear by it.
There is a whole DM subculture of just throwing out enemies randomly with little thought and seeing what happens.
Which is fine. However it limits the type of stories and memories the group can make. But if that group is fine with those stories, it's great but not everyone is.
Which goes back to my point about gauging and telegraphing.
One of the starter dungeons I run is one with 3 groups of antagonists fighting over the dungeons' resources with the groups of good guys.
One group is the Cult of the Crab. They are a group of weak common humanoid cultists. Fights against the mare slaughters if they can't swim away. The only reason why they aren't all dead is that their side of the dungeon is flooded in many areas. Therefore if they can escape there is no following them.
On the other hand the Blue Spears is a orc tribe run by orogs. Their section of the dungeon is well guarded and run like a machine. They have many anti-PC tactics drilled into them and many orogs have PC abilities.
So if you go through the contested areas dungeon, I roll a die to see which groups are in the area. A 1 gets you a cakewalk vs the crazed cultists in cloth and peasant weapons. A 6 get you the Blue Spears and the party better prepare to run once I mention orog.