[SOLVED] Why do we reinstall grub2 after fedup upgrade

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http://forums.fedoraforum.org – Just upgraded from F18 to F19 and it mostly worked fine. (Google online accounts won't work with two factor authentication even with the workaround http://kparal.wordpress.com/2012/12/...uthentication/) (Many - actually most - gnome extensions are quite unhappy - but OK probably get that sorted in time). But my question is - pros and cons about running grub2-install after upgrade. The instructions say to do this but strictly speaking it's not necessary as my BIOS system is booting fine without it (not UEFI). Also saw one guy ran into an issue doing this. Also if you do run it - do you (HowTos)