Based on your post, I guess you a newbie (like me) As mentioned in the two preceeding posts, rooting give you more option to "explore" your new toy. However, it will require spending more time to "experiment" and to learn
If you are only interested in watching movies, or listening to music etc ..from an external flash drive using the OTG adapter, then rooting is not necessary
I rooted mine and in the process I learnt a few things as well as screwing up a few times LOL... (fortunately, the mods in this forum quickly came to my rescue)
If I were to buy a NEW N7, I would not root it since I can install "Nexus Media Importer" to watch movies and reading ebooks ...... because this is all that I need
In summary, it a personal choice