Separate urgent from important, and notice how much of your week serves neither.
Use when Use it when you are busy but not progressing, when a team is permanently reactive, or during a periodic review of where a role's time actually goes. It works well as a recurring habit rather than a one-off, and it is a useful device for a manager and report to look at a workload together without it becoming personal.
Avoid when Avoid it where you have little real autonomy — telling someone to delegate work they cannot delegate is just a way of blaming them for their constraints. It handles individual tasks better than long collaborative efforts, and it has nothing to say about work that is important to someone else and not to you, which is most of what makes a job hard. It also assumes you can tell importance from urgency, which is exactly the skill people struggling with this tend to lack.
Observe, orient, decide, act — and win by cycling faster than the situation changes.
Use when Use it in genuinely competitive, fast-changing situations — an incident, a live negotiation, a competitor's surprise move, a crisis. It suits environments where information is incomplete by nature and waiting for completeness means losing.
Avoid when Avoid it for decisions that are expensive to reverse and slow-moving: a factory site or a pension scheme does not want tempo, it wants analysis. It is widely misread as 'decide fast', which drops the orient step and produces speed without judgement. It also has little to say where there is no adversary and no clock.