My personal opinion is that the legends were a little underwhelming. We had a nice/good cutscene with xerneas(i play x) but other than than that...
None of them. All of the Legendary encounters are stationary. Bring enough patience and Ultra Balls/Dusk Balls/Timer Balls and get your hands dirty. Save the Master Ball for something that really needs it.
Pff bump that I went ahead and used one on Zygarde since it's possible he'll have significance if there's a future installment.
Not as though it's going to get used for anything else unless you want trading fodder.
Which is why possession of the resource logically shouldn't automatically equate to use of it.
I never said it was necessarily something in X/Y. Possession of a valuable resource that doesn't expire isn't (shouldn't be) tantamount to mandatory use of it.