There is a theory that catch cans are a self fulfilling prophecy, in that they increase crankcase pressure thus increasing oil blow by and therefore you think they are doing you a favour. Who knows.
All i can say is that on my Td5, there is not a great deal of oil reaching my Intercooler and i have no catch can. Personally, i wouldnt bother fitting one, but some people swear by them. Usually Aussies for some reason? Maybe because they have all dusted their engines!