An advanced player is skilled at operating fighting games. With enough practice, even you have a shot at being one. This is not to say that you will ever be, or even have to be, as good as the regular tournament champions at Evolution or Tōgeki/SBO, but you can certainly try (maybe even succeed! I wish you good luck should you pursue this endeavor).
Unless someone has a particularly impressive track record, there is a fine line between an advanced player and an intermediate player. It is hard to tell the difference, if you can truly say there is one.
However, except for truly bad characters (or joke characters), there can be not-so-apparent good reasons to use them: when high-tier characters are not used absolutely perfectly, a hard-to-use character may succeed against them quite well.