If you have a mobile nutrient deficiency (N, P, K, Mg, Cl, Zn and Mo) the plant will pull the missing nutrient from the older leaves to supply the new growing tips (causing your old leaves to yellow/brown). They're called mobile nutrients because they can move around within the plant. If you pull the large fan leaves, which contain these stored nutrients, then your plant will just start pulling the missing nutrient from the next set of green leaves and they’ll start yellowing/browning and you'll be chasing your tail with the plant looking worse and worse. It's best to leave the old leaves attached until they are completely depleted of nutrients (at which point they’ll pretty much just fall off the plant).