This is a great reference for high-level functionality in workforce planning solution. I would add sourcing strategy to fill gaps. Talent management is discussed, but determining if if the right source is internal, new full time hire, part time hire, contingent worker, etc, is also important.
The intro says it all: "Effective performance management is not the result of a well-written review form, or even an expensive software solution. These are tools that can help, but they won’t magically make all of your managers experts at delivering performance feedback."