What's the benefit of playing fretless? It's a slightly different beast and you can get different tones and effects on it that you can't totally replicate on a fretted bass (the reverse is true too). It may improve your ear, you may find it easier to play. I love the tone and like the feel of it. Plus, I get to try and emulate Pino, John Giblin, Mick Karn, Tony Levin, Larry Klein, etc (not necessarily with any great success, but I try).