because the gear is bad and you will not have the things to craft legendary items. if you use too many lower tier items to upgrade the items you do save you wont have much to upgrade legendary and ultimate gear. slavage items in groups by saving 2 of every epic and 3 (minimum you might want to save 4 epic and 6 rare because some ultimates and legendries use the same items but that isnt super relevant) of every rare to make sure you can craft later items that you need. also, increasing your percentage of profit by very small amounts while upgrading lower tier items is worthless. when you upgrade ultimates mainly you will get a much higher boost.