Several years ago, for TFS, we adopted a cadence of a major release, followed by a couple of significant feature releases, followed by one or two releases which contained mostly bug fixes. The major releases were typically ~18 months apart and the minor releases varied from 3-5 months apart. We made some mistakes along the way but, overall, the cadence has been working reasonably well.
Today we released the release candidate for Team Foundation Server 2018 Update 1.