Actually conformation is very important...
When body parts are in correct positions, and the angulation of the dog is correct, it makes the work more efficient. So a dog could have all the drive/energy in the world and if it has the wrong conformation it will be burning more energy moving than a dog with correct conformation. Correct conformation also makes a dog less likely to get injured.
What you have to remember about conformation is that you should look at what is actually written and not how people interpret it depending on the lines they're breeding or their preferred venue. And yes...I understand that statement is contradictory because I'm telling people to have their own opinion on the standard rather than concentrate on how others interpret it.
So in the OP's opinion...a leggy, thin boned dog, has been proven to be more fragile when it comes to work (jumping and things of that nature). There are of course levels of leggyness and thin bones but in general that's why breeders do consider conformation.
CD RE TC HIC 7/10