Workforce planning, even if kept basic, goes a long way towards making sure you have the right resources, with the right skills, in the right roles at the right time.
Overly in-depth workforce planning can fail as there are so many real time factors which it cannot anticipate. For example, multiple level resignations in the same department or function where internal successors are depleted, employees personal preferences can change suddenly based on opportunities they never foresaw which are now visible to them, company mergers and acquisitions where new employees are available to fill future roles.
Start simply with identifying critical roles - those roles if they become vacant will have a significant operational or financial impact for your organisation. If it is found that there are no suitable successors available internally then decide whether to identify and start preparing someone internally or identify where affordable candidates may exist in the external labour market as a future resource.
Next can be key roles - those roles which are important to have consistently filled and which may require some specific level of education, a particular skill set, prior experience or exposures.
Remember that plans are never static and need to be continually reviewed and adjusted as your people and organisation develops.
If workforce planning is supported with individual career plans then you will be in an envious position where employees will feel valued and your organisation having the best chance for smooth people transitions.
Finally, keeping workforce planning basic and regular can deliver more relevant resourcing options at the time of need.