New Tags

Why is this necessary in the first place?

Why is it necessary for anyone to be able to post at all?
Why are any of the BBCodes necessary? All they do is stuff. You could type in plaintext just as well.
If you don't have a use for it, don't use it. Miracle of miracles.

It's not like it's going to stop anybody from getting to it if they want to, all they'd have to do is make a minimal-content post once in the thread.

Anything can be abused.
Anything can circumvented.
Neither of these is a newflash.
Neither of these is a reason why new things shouldn't be added.

I'm not trying to be all smug and argumentative

Then stop. Whatever it is you're doing, regardless of intent, is serving absolutely no purpose but being negative for negativity's sake.

You don't like it, you won't use it, the world moves on.
You're not exactly a prolific poster upon whom the entire forum pivots, now are you? I think we'll survive your lack of understanding.
If and when you find a scenario where it makes sense for you to use it, you can use it. Until then, it's just there. Like all the other tags and options you don't use every hour of every day.