Do you need to seal your paver? While it is highly recommened, the answer is no. You will get years of enjoyment out of your concrete pavers, even if you don't.
That being said, I recommend sealing because it protects them and helps them from fading. If you use an ice melter, even a concrete approved one, you must seal your pavers or they WILL spall on the surface, creating pock marks. Sealing concrete pavers also protects driveways from oil stains and patios from BBQ grease stains.
I recommend always using a solvent based sealer over water base. Solvents are easier to work with over time if there is effloressence or other problems, and it is easier to maintain.