Properly spaced sprinkler heads make a big difference in watering efficiency and effect.

Take a look at these examples:

50 feet spacing between sprinkler heads:
At 50 feet, the effective coverage of each head is out of range by 10 feet or more.
 
40 feet spacing between sprinkler heads:
At 40 feet, the sprinkler heads are still out of range by 5 feet or more.
 
30 feet spacing between sprinkler heads:
At 30 feet, the sprinkers are now head to head. There are no weak spots.
Result: even, effective watering of the lawn.
 
Residential sprinklers throw water approximately 25 to 40 feet. But with typical water pressure and volume demands when the system is running, average coverage is 30 feet.