You can easily make an argument for either side of this issue.
On the “boon” side, you can argue that mobile phones have made life more convenient for many people. They allow people to keep on doing business while they are on a bus or walking home. They allow parents to always be in touch with their children. They can even be used in developing countries as a way to store and transmit money from one person to another, thus making it easier for people to do business in such countries.
On the “bane” side, you can argue that they have taken away much of our privacy. We can no longer enjoy time away from work with our bosses unable to contact us. The signals our phones give off give a record of where we are and where we have been that the government and/or advertisers can use. We can also argue that they have made it less pleasant to be out in public. People no longer talk to one another but rather talk loudly on their phones, making public spaces much more annoying.
Thus, it is easy to argue this either way. Which argument seems more compelling to you?
The first and most important benefit is having a way to call for help in emergency situations. For example, if you were out riding in your car and broke down, you would have a way to call for help. If you stay out of the home a lot, having a cell phone will allow people to reach you if they need you. Most cell phones will have a built in GPS system. If you travel a lot, the GPS system will help you get to where you are going. Another advantage is that you do not need to have a landline phone in your home. It reduces the need for an extra bill and adds convenience to your life.