When you are doing your own home renovations there will be many jobs that require you to reach up to high places. Painting the walls and ceilings is just one of them. It is very important to have safe scaffolding for these jobs so that you remain safe while doing them, and so the jobs are much easier to accomplish.
Without scaffolding to support you, it is possible and even likely that you could have an accident or a fall, through overextending your reach on the ladder. In fact, the ladder is not all that safe whether it is inside or out. Inside, it can slip on the floor and outside, the ground can sink under one leg and cause the ladder to tip, throwing you off balance.