If you are using subversion, you should care about this. A lot.
A dump/load has potentially significant savings. In this case, copying our 1.8 ports repository to a 1.9 format repository:
$ svnadmin dump -q ports | svnadmin load -q --force-uuid ports2 $ du -sh ports* 22G ports 3.6G ports2 $ svnadmin -q pack ports2 $ du -sh ports2 2.6G ports2
For us, this makes it plausible to cache entirely in RAM for a lot more people than before.
For completeness, our other repositories:
$ du -sh base* doc* socsvn* 8.4G base 4.2G base2 632M doc 441M doc2 9.7G socsvn 5.5G socsvn2
Don't forget to copy across your hooks and configuration files.
For clarity, you do not get this with version 1.8 and earlier. Don't waste your time.