Xenforo 1.4.8. fixed a security issues for starters, not to mention the bug fixes. As a rule, it is always best imho, to use the latest version of whatever scripts/mods etc that you have installed in your server space.
I like that but the upgrade process here is so quick and painless and I trust these guys so I always do it. I have a good bit of addons and a one-off theme and nothing has ever broken. I started on 1.4.4 and each upgrade to 1.4.9 took a couple of minutes tops and everything works.