SD cards have a limited (huge, but limited) number of write cycles.
The best plan is to back up any file you don't want to lose. That includes all your contacts (if they're entered as "Account" contacts, they're backed up by Google at
Google Contacts) Texts (I use SMS Backup+) pictures, videos and music (just plug the phone into the computer and copy the files and, at least once, apps (use a backup program like App Backup and Restore and copy its backup file to the computer). And copy anything you add, at least once week. If you're near the computer when you add something, back it up at that time.
It's not only a failure of the SD card - you never know when your phone will be destroyed, lost or stolen. Insurance can replace the phone, it can't replace the files.
There's an old axiom in the programming world (pregramming humor is often backwards) - any file not backed up to at least 2 independent devices is a file you don't need. Why 2 independent devices? Say you have your phone plugged into the computer to charge and there's a huge power line spike. Both the computer and the phone are destroyed. Dropbox (which can be considered a device in this case) won't be affected. Most corporations use off-site backup. Everything gets backed up (after close of business every day if they have a good data policy) and it's picked up by a truck from a company that does data storage in a location that's pretty bomb-proof. A phone cll and you get yesterday's backup delivered, a few hours of restoration and you're back in business. Even if your building got destroyed. (Think 9/11 - there were a lot of financial and insurance companies in those buildings - that didn't lose a bit of data.) Your data may not be that important to that many people, but you can never take pictures of the baby's first steps again.
