I think a couple of reasons to buy sand for a propagation bed is that it is generally sterile, and free of weeds. If like me you have sandy soil, you could fill your propagation bed with
native soil, keep it covered with a plastic mulch for 2 months cooking in the sun before using it. I am trying a new way to
root cuttings, from honeyberry to
apple scions to peaches, I will post pictures of them if it does work. (no luck last year)