If you understand a concept, then you can reason its big O. Memorization implies a superficial understanding that may be revealed later.
Interestingly enough this works both ways. To say more accurately, memorization MAY imply superficial understanding. Memorization (and associated intuitive pattern-matching) may also lead to understanding.
A cheat sheet like this is also good shortcut refreshing one's memory of the concepts if this knowledge is not used on a regular basis.