Ugh, I could never get the hang of the battle planner in HOI4. You're a general. Command your soldiers!
I mean, I'm not opposed to it as an option. I would, however, appreciate not having to do it to get bonuses for forward planning, and would like to avoid having the AI constantly seizing control away from me because it disagrees with where a particular unit ought to stand. This may be me just not being very fond of HOI4 in general.