It turns all your cards into one creature type, which makes it easy for you to take advantage of the support cards for whatever creature type you name
While instant speed is great it turns out that the tapped clause is a nightmare for loads of reasons
They can even be attacking players or planeswalkers that weren't being attacked
If you just Brainstorm without a shuffle, youre not getting nearly as much value because youre locked into re-drawing the cards you tucked away
It doesn't copy whether that Equipment is tapped or untapped, whether it has any counters on it or any Auras or Equipment attached to it, or any non-copy effects that have changed its types, color, power and toughness, and so on
Because sacrifice is a standard keyword action, there is no perfect strategy to handle all sacrifice cards