A Simple explanation is that "like attracts like" and a Clearing Allows someone to Attract their true Essence as opposed to a Build-up of what You Can Call "Splat bug" in the Road of Life. (We all have it. We all get some garbage every day. This is the nature of life) The more we clear the truer our "vibration" is. So when we go around life we shine and attract what is our true essence and ultimately our life purpose. This also has the benefit of making us truly happy.
Another way to think about it: Imagine that you are carrying around your garbage bag wherever you go. It is not pretty, it smells bad and it is probably going to attracts rodents, insects, bacteria etc... (we call it bad people, users, abusers, selfish people, situations and events that are not aligned with what we want etc..) But we are used to this garbage bag because we have it every day and it is a part of us. "This is MINE." A clearing usually would "show you" your garbage bag (gaining awareness) and it will also allow you to clear it (sometimes by letting it go completely "I don't need this kind of garbage in my life!" or at least getting rid of the most smelly pieces in the garbage collection bag.) The funny thing is that people get so attached to their garbage that they might even get aggressive when someone tries to remove it, or get sick, or whatever. This is why we say "fill the space with light" so we do not miss the garbage and pickup something else to replace it in the bag of garbage. The more light we have the less garbage we carry because we see it and once we see it we are smart enough to not want to carry it around anymore... The reason we need the clearing is because well... we cannot always see our garbage. it is carefully hidden away from sight. The problem is the it is always there and it follows us around. People see us and step away because we "smell" bad and we have no idea why we are not attracting the people we want in our lives.
One thing I would like to stress is that we are not bad people or that we are not flawed or broken in any way. We are just people who are committed to improving our lives and the world and we want to do it without having the load of the garbage bag we carry around. This garbage bag is useful. It allows us to navigate through life fast. We don't always have the time to process things as they happen. This is why for example a daily meditation or spiritual practice helps because it allows us to clear the daily garbage and replace it with light. Also there is some we collected early on in life (especially as we were growing up) and we were too little to even process it with our rational mind. Trauma is also a great way to collect a huge pile of garbage.