If you are responsible for data backup at your data center, it's really worth knowing about a very cool technology that is built into Bacula Enterprise Edition called "Progressive Virtual Full" (PVF).
PVF allows you to you save significantly on time and disk space on the local storage, using some very clever Index management techniques. Without Progressive Virtual Full, the new full remains large (as in the picture above). With PVF, you save on the time to read the data locally, and the time to write the data locally. Just click on the picture to see what happens to "full 2", using PVF.
BTW, if your data has good deduplication potential, you save even more space. Amazing.