You can save lots of money, save the environment, save your septic system, and save your health by making your own laundry soap. 
You can save lots of money. The liquid version of homemade laundry soap costs about a penny and a half per load. Even on sale and with a coupon, you are not likely getting the cheapest of the cheap THAT cheap. Those savings add up over the course of the year. And when you run out, you can just whip up another batch, likely without going to the store!

You can save the environment. Well, you can contribute to saving the environment. Each time demand is created for another plastic bottle...and laundry soap jugs contain a lot of plastic...fossil fuels and dangerous chemicals are used. Also, that soap, the bottles, the labels, and the finished product all need to be shipped, using more fossil fuels and polluting this planet even more. Although we can't get away from using gas and plastics completely, we can reduce our own use of these items as much as possible.