The correct answer to this question is that we had a fairly long discussion on this subject back in September in THIS THREAD so this one is redundant!
I have read that sort of reply before, so does that make it redundant. To be honest Colin I remember old posts when pointed out but many new people join and just ask questions so I answer them.
I once belonged to a trade forum that encouraged people to search for answers before posting, the forum soon dried up and people lost interest.