Downside is if you ever run out of space when thin provisioning.
Bad things happen if you run out of space !
But yes, you can and ( I say ) you should thin provision.
It'd be a very good thing to have a thorough understanding of thin
provisioning in a NetApp SAN environ before doing so. You may
wish to take a look at:
http://media.netapp.com/documents/tr-3483.pdf
I hope this response has been helpful to you.
At your service,
Eugene E. Kashpureff
ekashp@kashpureff.org
Senior Systems Architect / NetApp Certified Instructor
http://www.linkedin.com/in/eugenekashpureff
(P.S. I appreciate points for helpful or correct answers.)