Lean says: Ideal batch size is one, and we should have Work-In-Progress (WIP) limits all over the place, as small number as possible, in order to minimize multitasking. The reason: multitasking is not as efficient as always focusing on one thing at a time because of the price tag of context switching, and therefore multitasking is a bad thing.
GTD (Getting Things Done, by David Allen) says: Always pick up tasks depending on context, available time, available energy and (lastly!) priority. This means lots of multitasking.
So which one is right? As in many cases, it depends.
Let’s go through these 4 aspects of GTD one by one and see some pros and cons regarding multitasking:
– Context: If the cost of context switching is high, for example you are a software engineer, and switching to another task means one hour extra work for you, as your development environment needs to be re-configured completely, the size of your WIP limit should be small and you should limit multitasking as much as possible. In other situations, this context switch may cost you only 10 seconds of time (for example briefly writing down somewhere a short summary of the status of your current task), and thus you shouldn’t worry that much about multitasking, but rather focus on the other 3 aspects.
– Available time: If you are a busy person having lots of meetings, and often have only time chunks of 10-20 minutes between meetings, you may work on many small topics, utilizing these short time windows, while some lengthier but more important task would need to wait a bit longer.
– Available energy: For example, if your current task requires intense concentration and intellectual heavy lifting, you may want to consider “taking a break” after lunch, and use food coma time for something that requires less of your brain capacity, like for example administrative tasks, or easier problems to solve.
– Priority: You may lose business opportunities due to completing already started tasks due to applying a predefined WIP limit instead of taking on an even higher priority task (that would represent the given new opportunity, or threat by the way). These lost opportunities or not handled threats are implicitly representing extra cost. Applying GTD you can actually solve this seeming weakness of Lean via keeping a small WIP limit by systematically putting lots of tasks in an „on hold” state in a managed way, but not only blocked ones like in traditional Kanban, but also ones that simply got behind in the priority list!
Even though GTD is more about the personal level, I think these can be applied somehow to the team level as well.