The recent discussion on Horse and Hound which I posted about last week had another interesting feature. The original poster could understand that horses with poor foot balance or neglected feet could benefit from time out of shoes but was asking about how it applied to horses who already had "good" feet.
Paul is a good example - his vet, farrier and owner had struggled with his lameness for several months but his feet looked perfectly competent - his vet had said he was perfectly shod and his feet looked pretty text-book. You could say the same about Big Charlie, Lady, Kingsley and Isha.
What these horses had in common though was that they weren't able to use their feet correctly - most of them landed toe first and in Kingsley's case he was having to adopt a twisted stance as a compensation.
For all these horses, their movement had been adversely affected and in the need to keep moving somehow, despite their problems, they had stressed and injured tendons, ligaments and muscles.
Often, the problem blocks to the foot, but the foot is far from the only part of the horse's body which is affected. Its why trimming is only a tiny part of the whole picture, and also why looking simply at feet is unlikely to give you all the answers.