Some of the more obnoxious sites won't let you read the full article (or any of the article, in some cases) without JS. Of course, you can just use some trickery to hide the overlay, but it gets pretty annoying.

For such sites you keep the button "temporarily allow JS execution" somewhere handy in your browser UI, but for more obnoxious sites you'll probably quit after getting bored from long loading time after getting used to how fast everything else is with scripts disabled :P

What's the advantage of using an add-on like ScriptSafe against just disabling JS in settings?

I use uMatrix for blocking scripts. By default I allow all 1st party scripts, and disable the rest. Then I can enable additional sources one by one if site functionality (e.g. playing YouTube videos) needs it.

The point is not to block JS completely, but to disallow it when not necessary (which it isn't for most of the time). There are plenty of legitimate uses of JS and keeping "allow JS on this domain now" button in accessible place is very handy.

Plus of course you can lift the restrictions selectively for each domain. From my experience it usually takes one or two domains to allow in order to get the needed functionality, and the rest (usually around 10) can be kept blocked.

You can whitelist easier and quicker and in some blockers you can block specific ad or tracker domains only.