Think about your daily routine, it likely involves a number of different activities that range from resting, to moving around and doing chores, exercising, reading, and of course sleeping. If you are using oxygen therapy at home your oxygen flow requirements may vary from the morning to afternoon, from day to day, depending on the season. Even if you need oxygen all day and all night the rate at which you need oxygen may not be consistent.
If you have more severe symptoms associated with COPD or you have overlapping conditions that restrict the proper amount of oxygen getting through your lungs, you likely need a continuous supply of oxygen flow. This means that you need oxygen delivery from your oxygen concentrators to be constantly flowing, even if you are not taking a breath.