You have to run the computation. Garry Kasporov is great at this. Its like what is the answer to 1 + 1, you can look it up in a table (memory) or you can understand the concept of addition and run the computation yourself to get the answer (best move).
Totally. Especially handy in openings.
/s
I don't see the sarcasm because it IS especially handy in openings. If you understand the core principles like developing pieces and taking space, you won't need to memorize any openings to become good.
It's not that simple, though. Even with solid core principles, there are lots of established openings where move order makes all the difference. All other things being equal, the player who has memorized a bunch of standard openings will have a distinct advantage.