What is the advantage of submitting to directories?

[perfectbazar]

Directory Submission is help you getting SERP and Back Link.

[Alexpatel1]

I also can't understand basic concept off directory submission because have some question here in my mind always,

Directory always have n/a PR - link page where approved our link
Directory not cached - link page where approved our link "means- Crawler is not following on that page"

So not counted in back link of our sites, but little bit countable.
so why we are wasting time more and more in directory submission.????????