Sprinkler Daddy Says:
Dry spots suck.

Why Your Sprinkler Design Has A Certain Number Of Zones And Sprinkler Heads

It would be really cheap and easy to just put all your sprinkler heads on one zone, but your system would be highly ineffective.  The more sprinklers you put on a line, the less pressure each head will be able to produce.  That means that the sprinkler heads won't be able to spray as far as they are designed - leaving dry spots on your lawn.

Sprinkler Daddy incorporates the size of your water supply line and the amount of water needed by each sprinkler to determine the proper number of sprinkler heads to put on each zone.  This ensures that you'll get the best water coverage possible.