Yes and no. The pre-made tapered leaders you see on the store shelves can be used right out of the package as they will taper down to the tippet diameter you need to attach your fly. After a few fly changes, that leader will shorten in length and the end diameter is going to be too large for what you need. At that point, attach a new section of tippet in the diameter you need and you’re good to go again. The tippet is going to get you the proper diameter of line for the flies you’re using. Check out my post on fly fishing leader and tippet to learn more.