Enable/Disable button is used for enabling or disabling a schedule. A disabled schedule will not be executed.
When you do not want schedule you may disable it or delete it. If you delete a schedule and need it again you will have to create a new schedule and configure its time and other setting, however if you disable a schedule, and you need it again, you may just press enable button. This will avoid you hassle of deleting and creating schedule every time you need or don't need.
Apart from it, one time schedule (when repeat checkbox is not checked) will be automatically disabled after executing first time whereas repeat schedules shall remain enabled unless user specifically disable/delete them.
Hope it clarifies the purpose of Enable/Disable option. If you have further queries, please feel free to ask and our support team will help you