To me the best advantages of Cloud services are that all my digital content is backed up in on place and I can access my photos, videos and music with all of my devices - smartphone, tablet and PC. I can also allow others to access some of the content to share photos for example. My TV can also access my cloud service. On a trip I could take picture using my smartphone, load them on the cloud and at home my family can see these pictures moments later.
Cloud services can also store your android apps, contacts and calendar - creating a google account will allow you save and access all that information by simply signing in. I change phones every 3 months and use multiple tablets for work and when I get I new devices all I need is to sign in my google account and all my information is available instantly.
Some cloud services are free, while others offer a free trial period after which you will be charged according to the size of your storage space.