Scheduling allows you to run your backups automatically on a regular basis to keep your backup data up to date. Most backup tools will allow you to run backups in the background on a recurring basis, with shorter or longer intervals depending on how you want to use the tool (e.g. continuous, daily, weekly or monthly).
It may also be useful to consider some advanced scheduling features, such as only running a backup when the computer is not in use, and preventing the computer from automatically powering off or hibernating before a backup completes.