I don't like trimming them off any more than I really need to, so as long as the cases aren't over SAAMI spec or too long to for the chamber, I pay more attention to keeping the lengths equal. If the lengths start varying, I find the shortest case, then trim the others to match it. If they get up to SAAMI max or are getting close to being too long for the chamber, then I will trim them back about .004-.005"