When painting a wall to ceiling with 2 different colors, you want professional results and a super clean and straight line. I love this edging tool that helps deliver straight lines. This video will show you how to use the painting cut in tool, and what to watch out for. This will help you paint straight lines without tape. Depending on what you are painting over, you may still need to touch up a few spots. This video shows painting straight lines over fresh texture which is a slower process.
https://youtu.be/S_6HOFSSFzA