I recently had a bike fit done at Bicycle Richmond. It took a little over 3 hours and covered everything from arch support and cleat location through crank length experimentation, saddle experimentation (both the position and the model), and then front end stuff. Saddle position movement (down and forwards) basically cured the hip issues I'd been having on my bike and stopped me riding for approaching a year, the new saddle is more comfortable to sit on, and the reach adjustment (stem and bar change) means I ride on the hoods and not just back of them. We decided not to change the cranks - 172.5 is OK for me (6ft), and my hip RoM is fine, I was just hyperextending the right leg. I was kinda expecting to go down a fair chunk, but we tried it on the jig and found no benefit.
If you are having issues, especially if they relate to your feet, and you can afford the £300, I would highly recommend them.