Must parents be "on the same page?"

There were times in my parenting when my husband and I were not "on the same page", as the saying goes. What helped us get there was learning that we needed a common set of principles by which we wanted to raise our kids. This took a while: I was parenting in duplication of the way I was parented; he, in reaction to how he was raised. Deciding on a common set of principles helped us come together in our parenting. It also helped us get back on track when things got off track. So do parents have to be on the same page? I don't think this is always possible; there are times when one parent is going to have to stand aside and let the other parent take over; but knowing that the other parent is using a family principle in their parenting makes this easier.