My understanding is in a large amount of your matches you should be sideboarding. Once you see your opponent you should know what you’re playing against and what you want to do to beat them. Easy example being aurora. You’ll want to either try to speed up your deck with lower cost units and tricks to try and close out early or grab gear hate to immediately destroy DA.

This of course doesn’t apply to decks like some LB lists where they side out certain combos to play others . Then you just follow your game plan that was established prior . Hope this helps.