If you are not aiming for a particular morph it is ALWAYS better to breed unrelated individuals. When you breed two individuals that share the same genes you are more likely to get recessive traits. Some of these traits can be desirable, which is why some people say it ok to inbreed. But other traits are not desirable, causing mutations or deformities. I believe that even people that approve of inbreeding will not do it for more than 3 generations without adding some new genes. This tells you that it is not a good idea unless you have a good reason for doing it, like trying breed particular colour morphs.
Coming from a scientific background with knowledge about how genetics work, I would personally never inbreed any pet (whether it is a snake, lizard, dog or cat) if i could possibly help it. I'd rather go through the effort of selling one animal and buying another with new genes....