The key is commonly used. I don't think I have ever needed the square root of 3 in a context where I wasn't using a calculator anyway, so memorizing it would have been far more effort than looking it up (since any calculator can look this up instantly). Does it matter who the leader of China is - for some people it does, for other it is trivia not worth the bother of looking up. Back when I was getting my degree 7x8 was important to know (even if a calculator was allowed doing the math mentally was a trick I learned - most college calculus problems are selected to have easy math so if the math is hard I probably need to back up a step and fix my mistake - this trick didn't apply to other classes though), now it is mostly useful in context of proving to my 4th grader that I can do her level of math (7x8 might come up in real life, but only in contexts of a much harder problem so I'd be using a calculator anyway)
