This table should explain things. Since you don't need to bother about bones/food, them auto attacking you or high defence armour, you can get more kills per hour. The profits are less per kill, but since you get more kills in the same time the profit is greater. You easily pay for the supplies with just the coins you get from high alchs, the only disadvantage is that you have to bank sooner, but this allows you to bank herbs and other drops you would otherwise have to drop to make room. Yep, herbs make quite abit when you start picking them up.