Water, time & $$
Here in So Cal (with heavy clay soil) I save all my cumby plastic nursery pots and every time I plant a new plant, I "plant" a pot nearby. Then when I water I fill up the pot in the ground and the water slowly seeps into the ground. I get deep watering, while saving water time and money. It's worked great for me - and if i get bored of the hole it makes a perfect nursery for a small annual.