DBA set up: Pay Period of the month = * ... Any issues with this?

 In the DBA set up, when you designate which payperiod of the month this deduction should be taken, have you ever seen any drawbacks to putting a * in there to be calculated during the first period worked in the month?

For our union dues, they are to be taken the first pay period of the month, or, the first pay period of the month the person actually works. We currently have Pay Period 1 set to Y, but in these days of fluctuating work / workforce it seems like we would be better served to have this set to a *. But I swear we had it set that way previously and ran into some issues, therefore switching it to our current set up. However I can't recall what those issues may have been. Do you see any drawbacks to