What's the point of Cull?

It's not too bad on champions that play passively earlier, or don't need the extra HP as bad.

But, to be honest, it's only good if you're actually good at farming. If you're someone who can't hit 70 cs at the ten minute mark, you probably shouldn't bother with cull.

i feel if you use it right you can sustain longer. especially on bork adc which will take cutlass asap

you don't get it early, after you have some items then get it because the 100 gold plus 300 bonus with the selling price gives you 460 gold. So, its now worth it really just like the new jg item