Purification methods and knowing which to use (A level)

Hi, I am confused as to how you know which purification methods to use. For example, an exam q asked how you would purify a sample of benzoic acid (which is insoluble in water) and the ms mentioned recrystallisation. I don't understand why you wouldn't use a separating funnel - surely the product is insoluble to you could remove water soluble impurities.

I basically dont understand how you work out the order of purification methods to take e.g. recystallisation then washing then drying, and how you know which to use. my textbook says recrystallisation is used if the product is a solid, but does this mean the solid could be dissolved in water?

Many thanks