Id VS class selectors. Which is better to use?

Question

I have read in other course's discussion that using id selectors is not very good practice and that one should better use class selectors. But there weren't clear explanation why. are there any difference in use if these kinds?

Answer 1

There's no downsides to using either. The problem is that if either is used to much, the page becomes completely black on paper.
Still, it doesn't hurt to use either, make sure to properly guide the browser down the right path when refering to them.