There are many reasons why knowing, understanding, and applying knowledge about impermanence in our lives is beneficial.
We all tend to take things for granted and we might think that our life will carry on for a long time. Such an attitude might not be so helpful, particularly for practitioners. For instance, when we are faced with difficulties in our lives and come to our senses we start to act in the right ways and with a sense of urgency, but then sometimes this can be a bit too late to make things right.
Opportunities come and go, but nobody is able to predict how long we are here, and as much as possible, we have to always be mindful and alert so that we can grasp every beneficial opportunity. Therefore, as many Kadampa masters have said, we might not save the fire for the next day since nothing is changeless.
We all might live very normal lives, but at the same time, we cannot afford to forget that change is here to stay and we have to simply learn how to live a beautiful life in these always-changing circumstances.