I took my A3 2.0 FSI in to replace E.G.R. Valve as instructed by the AA. But while the car was there, the Garage said I need to change Camshaft Control Valve as well which cost extra Ł140. Not much information was given.

Can anyone tell me what is what does Camshaft Control Valve does exactly? and does it normally need changing from time to time? My car has done 90,000+

Thank you in advance!