How important is saving interest?

I would guess being able to manage your economy properly adds 2-3 to your average finish. Some games RNG is just not on your side and you're unable to pick up even your core items, or you reroll to get the key piece of your comp and and fail to grab it, but being able to econ properly will end up being the difference between 8th place or 5th place, or between 4th place and 1st or 2nd place.