It's the same thing as having bad front end alignment in your car. If the insert and shaft aren't perfectly true with the broadhead then it will wobble when the shaft is spun. You want to be sure that this doesn't happen or the arrow won't fly true since the broadhead will be steering the arrow off center. This is the reason for trueing the ends of your arrows before installing your inserts. If your broadhead alignment isn't true you can switch heads until you find an arrow/head combination that is true, heat and rotate the insert (if installed with hotmelt) or retrue/ camfer the end of the shaft (if using HIT arrows).