I iron, steam and spray my (pre-washed) fabric before cutting. During and after piecing, I steam press to set the seams because the up/down motion is faster, but generally iron after that's done.
'Press don't iron' is a rule I choose to ignore because doing so works well for me. It has never distorted anything, not even bias edges since once they are seamed they don't stretch. Possible contributory reasons might be the hot water pre-washed fabric and on-grain cutting/piecing/ironing.