I came from a sailing/racing background, and figured it would be easy to make the transition to a windsurfer... wrong.. I spent at least 12 months trying to decouple everything I'd learned about sailing and re-learning how a windsurfer works.
In hindsight if I'd gone and had a few lessons, I'd have probably accelerated through the learning curve of footstraps, harness, waterstarting and maybe even gybing... having said that, I did get some satisfaction out of being self-taught umm.. with the help of "Beginner to Winner"

Back to your question though, I don't think you really need to understand the basics of sailing for free-riding, as long as you know that the wind comes across your shoulders to make the board go...
So I'd say for:
Quick improvement, ignorance is bliss ie any other background than sailing.
Safety - surfing background for any beach-based sailing (rips, waves etc), and sailing for restricted waters (ie having to know your marine navigation rules and the like)
Performance - depends on what you call performance? but rigging a windsurfer sail is completely different to tuning sails on a yacht, skiff, or dinghy.