This of course depends on your data, but for the home user who generally stores photos, videos and music, 99.9% of the changes consist in adding new files. Thus

This of course depends on your data, but for the home user who generally stores photos, videos and music, 99.9% of the changes consist in adding new files. Thus any modifications of an existing file are somewhat suspicious, and keeping also the old version in your offsite backup is a very good idea and essentially won't increase the storage requirement. E.g. with rsync, you use the --backup and --suffix flags.