Use yoga props instead of Pilates equipment when the session needs support, reach assistance, comfort, alignment help, or pose access rather than guided resistance or apparatus-based movement. Props are usually the better fit when the goal is to modify a position.
Pilates equipment has the stronger case when the workout needs springs, straps, rings, machines, or structured resistance. Yoga props are the simpler choice when a block, strap, blanket, or bolster solves the practice need without adding a full equipment setup.