Any wood with exposed end grain, especially upfacing grain without roof to protect from weather and sun needs a cap or protection from wicking water. White Cedar is known for durability and will last longer than Red cedar, or other species. Maybe long enough for you to warrant no cap. Any wood allowed to "wick" moisture will and eventually rot, split or need replaced.
Some of the "end seal" or wax products will help short term, but tend to break down with UV and contact. I like a metal cap, hammered, bent and cut around the shape of the post with small finish nails or screws (fastened on the side) to hold in place. Copper looks great, but is expensive if you have lots of posts. Galvanized and painted aluminum another option.