Why would I ever want to buy Corrupting Potion?

This thing is 500g and so ineffective at what it does. "150 health and 50 mana over 12 seconds. 3 charges." I can buy 5 HP Potions for half as much and get far more out of it. The burning effect is negligible. 15 damage over 3 seconds? Gee, that 5 damage per second sure is gonna give me an advantage in lane. "Halved for AoE and DoT spells." /sigh

I just...I don't understand what Riot was thinking by releasing this.