I don't know if this was already posted but this is a great article written to help explain the differences. it is from the APA-ABA Youth program http://www.apa-abayouthpoultryclub.org/Edu_Material/Easter Eggers vs.pdf.
As for the SOP, while you may not show or be part of the APA or ABA, they are still guide lines on what the breed is to look like and the function of the breeds. It is correct that not all birds of Breed A will match the standard not many will as these are supposed to be the Ideals for the breed, however it does give expectations. for example if you tell me that you have a Cornish to sell me I would expect a bird with a pea comb distinctive heart shape that is similar between the males and the females, tightly feathered. those images come because of a written standard. there are more breeds than are recognized or accepted by the APA or the ABA. But most breeds have a written standard somewhere other wise we have no identity to a breed. when I hear Cochin I think most of us see the same type of chicken, that is the true benefit of a standard.
As for the SOP, while you may not show or be part of the APA or ABA, they are still guide lines on what the breed is to look like and the function of the breeds. It is correct that not all birds of Breed A will match the standard not many will as these are supposed to be the Ideals for the breed, however it does give expectations. for example if you tell me that you have a Cornish to sell me I would expect a bird with a pea comb distinctive heart shape that is similar between the males and the females, tightly feathered. those images come because of a written standard. there are more breeds than are recognized or accepted by the APA or the ABA. But most breeds have a written standard somewhere other wise we have no identity to a breed. when I hear Cochin I think most of us see the same type of chicken, that is the true benefit of a standard.