By grafting higher on the rootstock, Poncirus is able to provide a bit more influence on the overall plant. Additionally, it raises the less hardy scion further from the super chilled layer of cold air that accumulates on top of snow cover on wind-free Winter nights.
I happen to have 1200 Poncirus rootstock plants in 3 batches of development, therefore it's my default "go-to" rootstock. Although most of these are smaller in diameter than my preference, I'm practicing my skills at micrografting them. The biggest drawback is that the process is slower than larger sized rootstock.
Having nimble teenage fingers would probably be an asset, but it's been a number of decades since I've had those!