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.