Explanation for Attack Speed Glyphs and Quints

So I noticed recently that the LCS players as well as certain youtubers are using/recommending 6 attack speed glyphs and 3 quints. I've always been using 3 attack damage quints and full magic resist glyphs, is it worth switching? And what is the thought processing behind it?

I can see how it would be good on Kalista with her slow autos and her auto dependency for movement, but why is it used for the other adcs?

I currently have the attack speed quints but I don't have the glyphs yet so i'm wondering if I should invest in them or farm up more for another champion or rune page (I have 5).