Overclocking will make your phone faster at the expense of battery life, and perhaps making the processor die prematurely (i.e. making your phone stop working; this probably depends on the extent of overclocking, and probably shouldn't happen noticeably anyway. Probably still last a good few years). And the "cons" of rooting AFAIK are if you're not careful, a malicious app could mess up your phone and steal more info than a malicious app on a non-rooted phone (but if you root correctly, you should have to give permission to any app to "use" the root), and it probably voids your warranty.