Slack isn’t waste, it’s spare capacity or buffering. Shit happens, so having room to react, maneuver and adapt when something unexpected occurs can help protect deadlines (to a degree) and avoid potential catastophes. Tom DeMarco refers to this room as Slack . Kent Beck has added a practice called slack to Extreme Programming Edition 2 that advocates including some minor tasks in each iteration, which can be de-scoped if the team falls behind. I’ve also used slack as a feature buffer comprising low priority user stories.
In Lean Development waste is typically any of the following:
- Partially done work
- Extra processes
- Extra features
- Task switching
- Waiting
- Motion
- Defects
