The biggest advantage I've heard people give is performance: it usually wins all the benchmarks. The second is that they are usually further ahead with supporting newer hardware features inside the VM (e.g., 3D acceleration). The downside usually is that it's either not as robust or not as "correct" - particularly with their drivers. Not to say that it is unusable (it is plenty usable for most people), but it has more edge cases where things don't work right. Say what you want about Fusion but it uses the same virtualization engine and drivers that they use in their enterprise products. It's reliable as shit and behaves as expected when doing systems level work. It may not support all the cool features, but what it does support works well.