With wind pollinated trees like Chestnuts, spacing can impact production. With insect pollinated trees like apples, you don't really have this consideration. Things to consider when deciding on spacing:
1) Crown interference at maturity. This is based on the level of dwarfing rootstock.
2) Equipment access. Depending on the size of your mowing equipment, you may want more or less space to make mowing easier.
3) Hunting considerations. Several groups of more closely space trees with space between each group can make hunting easier.
4) Disease and insect damage. In some cases more space between trees can reduce both.
Just some things to think about...
Thanks,
Jack