Have you ever used a very accurate high quality machinists level? If you have, this might be easier to understand. Rolling the ball is way more accurate than some 4 foot carpenters level. But not nearly as accurate as a good machinists level.
So that is why.
KMRUNOUT
I am not debating this but the surface of a pool table is imperfect due to being covered in fairly thick cloth. You can set the level on the table three times and get a different reading.
You can press it into the cloth and get a different reading. Once you have a reading you still have to now adjust the table and get yet another reading. Just depending on the level will drive you nuts and when you are done.
Even a guy using a level will have to check his work by rolling balls. No table mechanic would level up a table with a level and then say, "It's perfect, I am leaving now". His phone would be ringing before he got a block away unless he got really lucky
Once you know the method rolling a ball is very easy and accurate. You can roll the ball three or four times in one pattern and see what it does and you know exactly what you need to do and how much. You can tune the table right in so to speak.
