Say I want Activity Stream view, Forums view, Forum Topic view, Leaderboard, Events, etc all to have a common set of blocks, I have to go in and customize each individually and ensure there's consistency. If I add or remove a block I have to manually go through all of them. And if I have several sites then multiply it by N. If I add a new page or new app then I have to go in at every level of the hierarchy and add them manually there too.
Agree on DB driven Pages you have common templating you can apply. I guess this is the same in principle except it's for those apps outside of Pages.