It allegedly helps improve the accuracy of locations services. That is the message that you'll get if you were to attempt to use the Maps app's voice guided navigation feature with Wi-Fi disabled.
Anyway, check out this answer: If you're not within a clear line of sight to GPS satellites, your device can determine your location using crowd-sourced Wi-Fi5 and cell tower locations or iBeacons.
source: iOS 7: Understanding Location Services
Thanks! That means I can safely turn it off. Great.