I think the intention of minefields is that they function as part of the Ost force as a whole, ie you place them to cover some of your flanks and close down how many angles the enemy can approach from, this works as a force multiplier and also means the easily spottable mines can be protected from sweepers by close by units. Synergy with wire, bunkers, MG42 etc.
Sneaking pios onto enemy retreat path to place mines is borderline abuse imo.
