They can be helpful in case of emergency or just for a chatting with friends. Modern smartphone can also allow to surf the Internet and use a lot of Apps.
But cell phones are not always helpful. They can be an obsession, some people use them a lot. Of course with all these social there are some risks to give personal infos.
Cell phones radically changed our way of life. You can use them everywhere and for everything, from a selfie to a front-end developing.