A backup of an Internet site is a copy of its content, which is kept on some other hosting server and could be restored if something happens. This feature is very efficient, considering that you can never know if a script update shall not go wrong or if you won't eliminate something accidentally - a file, a folder, a database entry, etc. If your Internet site is backed up, it may be restored the way it was prior to when the problem appeared, so there shall not be any damage, or at least it shall be little, depending upon the particular situation. Keeping backups on your laptop or computer is not very feasible, simply because you'd have to do it at least once a day and you could still lose info in case your last backup is not recent enough. In this light, you'll need to rely on your web hosting company, so you must double-check their policy on the backups, because some companies create backups only once a week, which will do no good if a problem occurs with a site that is being used and updated all the time, like an online store, for example.