Probably one of the coolest carry overs from macOS. iOS 11 can recommend how you can save space and help you take action from within settings. I assume this person asked because they needed room to upgrade to iOS 11 though. In that case, I suggest taking a look at what is taking up the most space and dealing with those factors individually: delete apps, offload pictures, etc. I’m not sure it is worth downloading an app to do it for you.