There are many Minis who are sadly lacking in their mare lines--I have encountered a number who have some great breeding on the male lines, but their mare lines are very weak. So, you've got a nice stallion whose sire is a well respected show horse. His dam is an average mare who is in turn sired by a big name stallion and out of a plain mare. Your stallion's sire is by another big name stallion--but his dam is a mediocre little mare off average parents...truly, I have seen this pedigree in a number of horses. There might be 3 or 4 big name stallions on the papers, but the mares are all mediocre. Some were perhaps bred because they had a well known sire, others I'm sure were bred simply because they were a mare and could be bred. This sort of pedigree is one reason why so many Miniatures do not breed true--in spite of several good stallions in the pedigree, with several poor mares in that pedigree there is a very good chance that any resulting foal will end up resembling one of those lesser mares.
I am so glad you brought this up. I have always been a pedigree hound, yet when asking about a pedigree, the owner has often told me they don't know or cannot remember, or sometimes even, that pedigrees don't matter. Pedigrees absolutely matter and that's a fact. The more you know about your horse's pedigree, the more you know about how you might or should, breed. Certainly, a few big names way back in later generations, don't mean a fig, except it's fun to know they were there. But the first few generations can tell one a whole lot about quality/conformation. It is obviously not always possible, to discover a lot about some or many, horses in a pedigree, but it pays to try to discover what one can about them.
That said, it does help to do one's research as far back as possible and to know about those horses listed. I can think of some big-name horses in several breeds, who now do in fact, appear way back in pedigrees. These horses were well known for carrying and passing on, some dreadful health and genetic issues, which we still see cropping up today.
So pedigrees are important. I see so many people purchasing a mare and immediately think of breeding her. Much of the time, they've only been in the breed for five minutes and I can tell, they've done little or no real homework on the breed, before jumping in and setting themselves up as breeders. I'm sure we've all seen on some all-breed forums, someone posts a picture of their mare and pictures of a couple of stallions. They ask which the membership feels is the best stallion for their mare. When asked if the mare and/or stallion have been tested for Frame, HYPP or Herda for example, they ask, "What is that?" They don't even know these problems exist in their breed and have obviously done no research, yet they are becoming 'breeders'. Makes my head spin.
Lizzie