If project prioritization is the Holy Grail of PPM, then predicting resource availability for project work is a close second.
On most knowledge-based projects, the inability to accurately estimate resources’ availability to work on project activities is as critical a cause of project delays as is scope/requirements creep or the underestimation of activity effort.
Most organizations start by having their resource managers SWAG availability for resources – these either end up being overly pessimistic or optimistic estimates and with each resource manager using their biases for these guesses the errors in estimation are heavily magnified.
The next step in evolution is to do time capture – regardless of whether this is done at a high or low level of granularity, and regardless of whether resources are encouraged (coerced?) to do it daily, at worst the information captured in inaccurate (as people forget!) and at best is historical (and hence suffers from the normal caution given to investors “past performance may not be indicative of future returns”).
The ideal solution is focus – have project resources work on project activities only and have separate resources to deal with operational processes and crises. This type of segregation is often impossible in certain resource areas, but strive for minimizing the multi-tasking that resources are forced to do.