I was surprised at how dirty the old filter was and having seen the state of it especially glad to have swapped it out. I suppose fuel tanks have vents and big openings for filling that lead to the ingress of dirt and grime. Petrol being a solvent keeps the dirt from sticking to the tank and the fuel pump sucks it on through to the filter. This makes the filter pretty important to keeping the car working properly.
Amazingly Volkswagen state that the filter on the MK3 golf does not require changing and should last the lifetime of the vehicle. If you look at the state of the one I removed off the car last year after 15 years you would probably disagree.