I use a similar technique on a server I work with. The primary benefit of this information is to be able to talk to business owners in a way they understand. You can get user buy-in for a data retention policy when they understand what it would cost to keep large amounts of old data online.

[begin example]

ME: Mary, we have been tracking database growth. According to this chart we project that we will run out of space sometime in mid-November. Our choices are to either add disk space or cut back on the amount of data we store.

MARY: How much will the extra disk storage cost?

ME: For $XXXX we can get enough extra storage to keep us running for another 18 months. Then we will have to add additional storage.

MARY: How about cutting back on the data stored? How much data do we store now?

ME: We have transactional and summary data back to 2006. If we only kept 6 months of transactional data it would allow use to run indefinitely with the current storage. We could archive the older data in case we need to pull it up again for some reason.

[end example]