I had a bike fit back in 2013 at a place in Shoreditch. All very scientific. After a couple of rides I was starting to get a pain behind both knees. I lowered the saddle by an arbitrary amount, and everything has been fine since. I wouldn't pay for a bike fit again, not for the type of riding we do. Indeed, when you hear of pro riders like Cavendish who is forever tweaking his setup, it does raise questions as to the benefits of a bike fit versus getting the basic setup right and then tweaking for comfort (or performance in his case).