silverpig nailed the soap thing.
Just make sure to use a natural, non-antibacterial soap.
Beer is food for soil life. Remember that there exists a very complex web of life surrounding plants. Something like half of a plants energy goes into producing sugars and proteins that are released through the roots to feed microbes and bacteria that live in the soil - they then break down elements(N-P-K-Ca-Mg-Fe) into forms the plant can use
Without these organisms, the soil would, well.. be dead.. and unable to support but the most adapted life.
It would be interesting to try and maintain an extraordinarily healthy lawn. I don't think I would bother, grass is just too boring. I would rather plant something cool.. some other ground cover.
Originally posted by: Skoorb
Something I've noticed and the guy across from me who's a landscaper does, is that if you mow the lawn really short, it will look a bit dead and yellow, but if it's got lots of sun and water, by the time it gets tall it will be incredibly green and nice. Then when it's time to mow you shorten it very close again and of course it looks yellow for a time, but then it's green when it gets bigger

Not sure what happens if you just don't cut it so short, but I like a nice short carpet-like lawn!
It is an illusion. It looks so nice and green because it was all cut short and yellow before.
When you cut all the green off the grass, it is an incredible shock. It'd be like seweing your mouth and your ass up for a time.

The grass grows very slow for a few days while it works to use every last bit of energy to produce some new green growth so photosynthesis can once again resume, and the grass can eat. During this time, root growth slows down and probably halts.
You will create much healthier grass if you leave some green. The grass will recover much faster, and it will never completely stunt it's growth.
The less stress a plant is subject to, the better.