Slack in your plans

Recent discussions with my colleagues showed that many software teams
still run into trouble because they pack too much planned
work into their iterations. Teams will usually run better when they have
deliberate Slack, as it allows their delivery to be more predictable and
gives them time to improve their environment.

While writing that bliki post, I also defined two styles of task
planning in agile projects. Timeboxed Iterations are used to
break up work into small chunks with a regular cadence to reassess the work
and future plans. Using a little ceremony around allocating work to
iterations helps make problems visible so that they can be dealt with
properly. Continuous Flow
dispenses with that ceremony, so skilled teams often prefer it.


Source: martinfowler