I had a bike fit at Wyndymilla near Farnham back in December, it was interesting and they just adjusted my set up, no need for new components etc. The saddle was raised a little, cleat position sorted and so on. But after a few months I wasn't sure it felt right when I got over 60 odd miles and I was adjusting things myself.
After a particularly painful ride I decided to call Wyndymill again, they said they'd have a look. This time it was adifferent fiter and instead of doing a fit on the jig and replicating these figures on my bike the guy put my bike onto a trainer and looked at it there.
Initially he adjusted everything back to the recomendations on the original fit and had another go. The saddle was raised about 4mm, he also suggested a slightly shorter stem and narrower bars, we tried ones he had to see how it felt and I cycled on the trainer for a reasonable time.
I was then given a couple of options, buy the recommended/sized kit myself or buy from them and have them fit it. They had cheap and expensive options for both bars and stem, the budget end was Deda and I went for that and they fitted the stem bars and new bar tape for £60, however the refit cost £0 and was pretty much a complete new bike fit.
It has made a difference, I did an 80 mile ride pain free, and reasonably quickly.
So in my experience a bike fit is worthwhile and you will need to change components if the ones you have are not putting you in the right position, however you should be given the fit dimensions and component sizes so you can source and fit them yourself. But if your bike fitter is sensible they should be able to offer you a reasonably priced option and then fit them and finally tweak the position with the new components fited.