If you have a hen that is still laying tiny after she has been producing for more than a few months you probably will not want to set hers as her daughters will be the same most likely. A person I know that raises Dorkings got their egg size up in just 2 seasons by only setting the largest eggs produced in the flock.
I've known people that did the same with different breeds and I read somewhere on BYC to always set only the larger eggs a hen lays. They said the larger chicks thrive better....
![jumpy.gif](https://www.backyardchickens.com/styles/byc-smilies/jumpy.gif)