Whether rankings matter, I think depends a lot on what your goal (as a student) is for going to college. Off the top of my head:
1- get a good-paying job post-graduation? : you want a school with a good reputation within your target industry (and here's where rankings play a big part)
2- actually get a good education? I'd look at the professors, curriculum, what student-learning opportunities are offered, etc.
3- enjoy the college experience as a young person? That will depend a lot on what appeals to you personally (i.e., big state school vs LAC)
4- study abroad / other opportunities?
5- an affordable option that doesn't put you in debt? This There's usually a trade-off there even if you get accepted into the school of your choice.
6- close to home (usually goes with affordability / i.e., you might be able to keep living at home)
I'd imagine that for most people it's ideally a combination of these, but knowing which is the highest priority for you personally is very important. And rankings don't really play a part in any of those except maybe for #1 -- and even then it's hard to know. Example, my D went to what might be a "tier 2" ranked U (top 50, but not top 20) which most people have never heard of but was well respected among employers in certain industries (engineering in this case), so your target major is a big factor with that. Also, she turned down a top-20 U because it would have put her into debt; often lower ranked U's, i.e., the next tier down, will provide more scholarship money to attract top students (based on SAT/GPA) away from the very top-ranked colleges.