I always swore I wouldn't trim Daisy at all because she is so beautiful with her long, silky hair. However, I did trim a tiny bit off her tummy feathers which were dragging the ground (maybe an inch or even a little less), and I trimmed off some hair from the back of her slippers. You know, the part that sticks straight out from the back of their paws? It just gets soooo dirty when we go for walks that I thought I'd give it a try with taking some of that off. It's not noticeable at all and it does make some difference in the greyness of her feet after a walk on our neighborhood streets.
I will never have her over-all trimmed unless she has a health issue that demands it, as other have said above. I have 2 fosters right now who are trimmed and they just don't look right to me. And their hair sticks straight out all over, making them appear even pudgier than they actually are. And an all over shave? No way. I don't even think they look like Cavaliers at that point. I rescued a Cavalier from a shelter that literally looked like a miniature St. Bernard. She was shaved to about 1/2 inch long all over. Yikes.
Occasionally, if Daisy has a "cling-on" (you know what I mean), I will just trim off that hair with the offending cling-on, figuring that was obviously the hair in harm's way. She is so hairy all over that no one would ever notice a little bit missing back there. Honestly, I have never had a dog whose tummy is even covered thickly with hair like Daisy's! Her markings aren't perfect, and she's too big, but she definitely has the coat of a show dog!
BTW, I looked at the picture of the Crufts ( or Westminster, I can't remember) winning Cavalier and I was kind of appalled that it was so obvious that his ears had been blunt cut! If you are going to have a breed standard that says no trimming allowed, then that's the way it should be judged. If I were a judge, I would have eliminated him based on that! He looked weird, sort of like a poodle or bichon shape in terms of his ears, IMO. I do not like the poofy ear thing some showers are doing with Cavaliers. I think they look much prettier with long, silky ears, not teased poofs on both sides of their head.
(Just thought I'd throw that observation in since we are talking about trimming vs. nontrimming.)