A 'guide' to the amount of time an individual/unit (Formation.) should be spending on Ops/Leave/Training etc. The idea being that the pain is spread.
However, if you are in a pinch trade, or have very specific skill sets, then you can end up deploying way more than someone else of similar trade/branch, but different qualifications. There has been some disconnect, certainly in the FJ sqns, whereby do training deployments (A few weather flying days at a different airfield, for example.) count as time away from base in the Harmony plan?