The optional updates will cover new feature, minor updates, minor bug fixes. Stuff which is probably worth having, but doesn't have a security or major system stability implication and hence is classified as optional.
I agree - I raised a couple of bug reports with MS about audio CD playback in Win 7 in 2010, which did - eventually - get fixed in one of the optional updates. I'm sure a lot of people must have raised it for them to have fixed it, but it shows that a) they do listen, and b) the optional updates are worth installing.
I scan ALL updates presented before installing, but I'm looking for strong reasons NOT to install, rather than the other way around.
SD