Do you prefer to push with the bow arm or not?

NO!  The bow arm (I think) should be set and essentially static.  When you talk about expansion, that is a motion produced by the string side shoulder that results in pressing the bow shoulder/arm out towards the target.  BUT absolutely NOT any muscle or bone movement on the bow side.

Expansion (for me) is the feeling of pressing my sternum (chest) out a little by ONLY pulling the string shoulder back and NOT the bow shoulder/arm.  That action will press the bow side out without any further bow side muscle activation.

Arne