Do you HAVE to use the FSS?
Not unless you actually want to discover new planets for yourself without spending hours using parallax, as already mentioned, in the hope of locating them. I do find using the FSS in the bubble to be a pain due to the number of USS's some systems have. Using parallax I expect you could find a lot of close bodies, but there are many even with the FSS that are hard to find, bodies not on the orbital plane that would be impossible to find without using the FSS.