Smashing is done post wod/last.
Smashing down regulates the system.
Part of the process of going from 60-0mph
It hits the parasympathetic nervous system.

If it is tender or irritated go above and below it.
If using a lacrosse ball it may be too hard. Try a Yoga Tune Up ball  or soft ball.

There are different approaches to hit the same target areas depending on the goal, what the person is experiencing etc. Not right/wrong just different ways given the situation and what is going on.