There is another advantage of an off-site backup
in addition to your home backup - recovery in case of fire, flood or theft.
Irreplaceable data - such as photos - should have 3 copies at any one time. E.g. local online, offline and offsite. Or disk backup, CD/DVD and offsite.
Don't forget that overwriting a backup set with current data effectively puts 2 sets of data at risk simultaneously!
SD