I have them on but pick and choose also. Find my phone needs it. Anything that shows you where things are on a map and things like restaurant finders, nearest store locators, etc needs it. It uses minimal data, don't worry about that.

Accessing Maps off and on to use it as a GPS doesn't use much. Just make sure you don't have an app that keeps it running when closed like I mentioned in another thread. Maps is pretty good but I find Mapquest more like a real GPS, voice directions etc, and their whole UI is nicer.

You can keep on eye on your data usage in Settings/General/Usage, scroll to the bottom. Streaming video like Netflix etc uses it up. youtube uses minimal. I find each minute is around 2M, HQ is a tad more. You can reset it on your billing date. I access mine through my ATT app.

Of course you'll only have data usage when not near WiFi. If you have ATT you can use their hotspots, most McDonalds and Starbucks have them. There's an ATT app for that. They have a really nice bar code/QR scanner app too.