So I'm reaching the 'end' of Sun. I know that I'll go up against Solgaleo in a bit... my question is should I battle him and try to widdle him down and capture him with an ultra..or maybe a timer ball and save my master ball?

Is there anything post game that I should save the Master ball for?

Sub question, what did you guys use your master balls on for X/Y, OR/AS, Sun/Moone?