I recently obtained a A320 rating at CTE . I have over 200 hours of flying experience .
I understand its a captains descision wether to leave the pumps on or off .
I tend to select them on if the TAT probe indicates above 20 degrees , and leave them all off if the TAT indicated is below 10 deg. This I think is to prevent cavitation?
If the OAT is between 10 and 20 degrees , as a captain , I can choose to leave some standby pumps off and the main pumps on . It works well in my experience .
As always, when you are an experienced captain , its your choice , not anyone elses.