Screen protectors are transparent plastics or tampered glass or some other form of material which are made solely for the purpose of preventing the screen of your iPhone from scratch and keep the screen intact if it falls face flat on the ground.
Does your iPhone need a screen protector? The screen of an iPhone is made with ion-strengthened Gorilla Glass which is hard to resist scratches and less shatter if it falls. However, at a point in time the glass won't be able to withstand any more scratch or fall, and if you keep your iPhone in your bag or pockets with keys or other sharp objects, the screen is bound to get scratched. So, based on the expensive nature of the iPhone and vital information kept on it, yes, you need a screen protector.
It's good to bear in mind that not all screen protectors are the same as there are many kinds of screen protectors and different quality. Most of them are made of a thin plastic sheet which is placed on your screen by using static electricity or a form of adhesive. The more expensive screens with high quality like tempered glass screen protectors or screen protectors made from other materials are scratch-proof and are recommended for people who know their iPhones fall regularly or are naturally exposed to sharp objects.
Another reason why you need a screen protector or cover is to prevent the screen from breaking when it comes in contact with any force. Your iPhone falling out of your hands or from the bed or table or you mistakenly sitting on it are common occurrences in our day to day lives. That is why some screen protectors like those made from other materials are guaranteed to prevent the screen of the iPhone from cracking if it falls or you mistakenly sit on it.
Based on the delicate nature of the new iPhones, you have to be extremely cautious with the way you toss your phone. It can't be thrown into a bag carelessly or put in your pocket while running around or carrying your child on your legs. Due to the slim nature of the new iPhones like iPhone 6 and 6 Plus, it is hard at times to remember that you have such an expensive phone in your bag or lying around while working so you could quickly hit it and crack the screen. If you wish to keep the screen of your iPhone intact, then you definitely need to get a cover. The use of a cover for your iPhone 6 should not be a problem because the phones slim nature gives it the same thickness with other smartphones and it still looks stylish. These covers help you spot your phone lying around and even keep it safe when you toss it into your bag where there are sharp objects.
Get a screen protector or cover for your iPhone and use it without fear of scratch.