Read the answers to this question: What's the difference between primary & secondary fermentation?
I am an advocate of not racking to secondary. To answer your question:
Advantages
(of not racking)
- Reduced risk of infection
- Don't need as many vessels
- More time for trub to settle (racking can disturb the trub if you have to move your fermenter)
Disadvantages
- Risk of autolysis (low IMO)
- You don't get to "play" with your beer
Bonus
I do not rack to secondary and still get very clear beer. After kegging I cool the beer to the low 30's F for a week or so to brighten. Crash cooling drops a lot of protein out of suspension. The first pull is pretty goopy, but the rest of the keg is pretty clear.
Pro brewers do this in a separate tank called a brite tank.
If you bottle you can get the same effect by racking to your bottling bucket, sealing that up and crash cooling it for a week in the bucket. Be very careful moving it, or bottle straight out of the fridge.
