I recommend reading through this entire answer twice. I find that the pomodoro technique is more effective for activities that are complex and require a lot of contextual focus. It is especially helpful for tasks that benefit from brilliant insights and constant improvement and learning, like programming, writing, studying, problem solving activities, or skill based activities. If you are doing simple things that are are easy to stay on track with or that you can't really mess up with poor planning or that don't benefit much from brilliant insights, or that don't really have as much room or need for learning and improvement, it is not quite as helpful or as necessary to follow the technique so strictly. When you first use the technique, what I just said seems completely wrong. For complex tasks, the ring interrupts your flow just after it really helped you get into it. It builds up your concentration and rhythm to the point that you feel you don't need it and it is holding you back. This is missing the point.
You are supposed to start each pomodoro with a 5 minute review. Then work for 15 minutes. Then review or repeat what you just did for 5 minutes. What? This sounds horrible! Only 15 minutes of actual work? How could anyone get complex, long running tasks that require a lot of context completed working that way? Allow me to explain.
The starting review helps you to get out of break mode, pull the context back into your head, and plan ahead a little. It reminds you of all the things you realized during the ending 5 minute review/repeat stage. It gives you a chance to benefit from what your subconscious learned while doing background processing during the 5 minute break you just finished. Personally, I don't always take a full five minutes for this starting review. I basically know when I am done and ready to plow ahead with the task. But it should not be neglected. Then you work concentrated for 15 minutes, plowing ahead. Then you do 5 minutes of review or repeat what you did. During the review/repeat you will likely realize you forgot some important details or did things in a less than ideal order. You are likely to realize a slight change in direction that will help you achieve your most immediate priority faster and prevent you from going down a rabbit hole. Brilliant solutions you could not think of before may suddenly pop into your head, or that may happen during the starting review. You can take notes of your insights or quickly change your work. Then you have the 5 minute break. Don't do anything mentally complex during your break. Relax or do something short and simple, like starting a load of laundry. During this break, your subconscious will process what you just did. This will enhance learning, improvement, insight, and problem solving. If you do it right, you should at times get random insights during your break when you thought you weren't working anymore.
If you read the book, there is a lot more to fully following the technique than what I described. But it is all designed to help you constantly stay focused on your true priorities, learn, improve, and adapt, all with clarity. You will learn how to break more complex things down. It helps you to make real world progress toward your actual goals every 30 minutes. The process sets you up to realize your misconceptions earlier on than you normally would.