The NHS Choices website explains the value of walking:
It’s underrated as a form of exercise but walking is ideal for people of all ages and fitness levels who want to be more active.
They suggest that we should apparently all be trying to walk 10,000 steps per day. However, the recommendations make it clear that even 10 minute chunks of walking can count towards your weekly exercise requirements as long as you are walking at a moderate intensity. Walking as part of your commute to and from work is an excellent way to ensure walking becomes part of your daily routine.
Our Journey into Designing a Walking App 