
You can withdraw from all or any Variety class but not breed classes, and where there is no breed class at shows on the group system to gain access to the group you would need to go in the AVNSC classes to qualify for group, at Non group shows any BOB or unbeaten dog can go through to BIS or BPIS, so from AV pup or AV gundog or AV Veteran, which is why at non group shows you will sometimes see more than one of a breed go through to the final.
I only ever withdraw from varieties if the judge doing group is different from the variety judge and I think I stand a god chance in group.
At other times I have taken the chance, won the variety class and still been able to go through, at others i didn't but wanted the variety Judges opinion more than the group judge.
Also I find variety class experience stands you in god stead if you ever get to go in Groups as your dog is used to being in with other breeds. Also gives you a chance to see other breeds get to know something about them and see how other breeds are shown, and how ans why they are different to your own breed.
I must admit the lack of Variety classes and different judges affects whether I will go to Open shows nowadays. I am not prepared to go to a show where I can only take my dog in one class, seems a waste of time and effort, same if all the eligible classes are being judged but the same person.