Nothing bad, if you use "bup" or "borg"; The latter has better delete support, so is a better choice for rolling backup if you sometimes delete data. "bup" has the advantage that its repo format is git, which makes it easier to hack.

Both use rsync-style deltas to only send changes, but they use a content-addressable scheme like git so renames are a small metadata change record.

Also, both offer ftp and fuse interfaces if you need to access an older backup.