When I do root, it will be for app backups, more thorough customizations, and trying out different ROMs. Ad blocking would also be a major plus for me.
I haven't rooted yet though, partly because my only android device so far (a somewhat obscure Samsung PMP) has a very small community and no U.S. warranty. I'm willing to wait a little while until I can afford something more mainstream, and then I'll probably root. Having access to Titanium Backup Pro might be the excuse I need to take the plunge.