If you use the target message, you must explicitly manage voice allocation yourself. This can work well in the case of an additive synth, where each harmonic has its own poly~ voice and you never ask for more voices than poly~ has.
When you don’t know how many voices will be needed and voice-stealing might be needed, the note or midinote message are easier to work with.
The difference is clearly seen in the example patch "stockhausen-studie-II.maxpat" located in the examples folder. If you unlock the patch and double-click on "StII-synthesis", you’ll see a poly~ playing the notes of the score. Double-click the poly~ to see another poly~ inside creating the harmonics of the sounds, using the target message.