Do I use the mobile data when I have wifi on (iPhone 6)?

[blowabs]

Just got 6

I thought that when you have wifi on cellular data is Never use?? no??
Help...only have 10gb a month.oping I would not have to go to 15gb [yeah ..I am a cheapie sometimes...lol]
help. Thank You!

 

[phreddyl]

Re: Just got 6

Apple describes the different settings better than I can Learn about cellular data settings and usage on your iPhone and iPad (Cellular Model) - Apple Support
Are you sharing the 10gigs? If not if you use wifi most of the time I can't imagine you going over that