Grafted Trees vs. Potted Trees
I've wanted to plant an "Illinois Ever-bearing Mulberry" and the nurseries that ship the trees offer the choice of a grafted tree or a potted one (more expensive and smaller in height). Is there an advantage to either one or will they be about equal as far as health and initial growth? Also, are the grafts always on to the same Mulberry stock?
CSU Extension has nothing specific on grafted mulberry, so I am inferring from grafted roses. All varietal fruit tree are grafted. The grafted tree is grafted onto rootstock of a different variety because rooting cuttings from your plant is very difficult, so grafted ones are cheaper. Own-root trees are always "safer" because, if anything happens to the top (like a very bad freeze), it will grow back from the roots as the same variety, whereas the grafted one will grow back from the rootstock. The potted one is on its own roots.
Here is an article on the science of planting trees.