The only reason I can see for rooting the Nexus 7 at present is for the OTG stuff to access external storage over USB (A glaring error with the current Nexus products). I had my nexus 7 rooted for this very reason, but actually found I have hardly used it, and, with the recent update to 4.2.2, it has gone back to being unrooted.
I thought I would be very constrained by the 32GB on the Nexus 7, and the 16GB on the Nexus 4 having upgraded from a HTC desire (32GB SD card) and an Acer Iconia A500 with 16GB onboard and 32GB card (Do not buy anything acer, in my experience you need to return it 2-3 times to get one that works, then it will undoubtedly break a month after your warranty is up due to shockingly bad build quality, I ask you, powerswitch on a tablet motherboard not physically fixed to it, saves how much? anyway, Never ever buy Acer! rant over.) I have found it is more than enough for me mainly as I have switched over from having music to using Google Play as all of it is now held happily in the cloud, though you do need to have an unlimited data plan, or never away from wifi, to really see any benefit.