I think if I started the week knowing I could use 105 I would use them far too quickly, then run out and feel deprived the rest of the week.
Using them daily means I am quite disciplined about it all, and as some days are a bit under I don't worry too much if I have the odd day where it might fall slightly over.
As has already been said though, I don't go out drinking, so perhaps this is easier for me.