Rsnapshot backup - how does it handle data?

I've set up my backup using Rsnapshot . After 3 days I have this:

196 GB	/backup

3	GB  /backup/daily.0
191 GB	/backup/daily.1
2	GB  /backup/daily.2

Why is the 2nd backup the one with most data (191 GB)?? My expectation was that first day the backup would be huge, but then every next backup would be small as only diffs are saved. How does the Rsnaphot handle incremental backup data?