The first time I think I heard about it was from David Allen’s book, Getting Things Done.
The idea is simple, “if anything is going to take two minutes of less, do it because it is more efficient than input the task on the system”
This is a really powerful rule, because allow us eliminate an incredible amount of things from our systems and our lists, but require that you are paying attention that you are doing the important ones and that you don’t spend the whole time only doing two minutes tasks or worst that we forgot what we where doing and spend the time doing things that really had no importance.
We need to pay attention to the two minute actions, because as it is possible to save a lot of time, it is also possible that we waste a lot of time that we could have used for more important things.