Sumou is a Test of Power. Therefore you do it to prove you are stronger than your opponent.
You must Prove Yourself. Winning just by itself doesn't guarantee you've proven yourself. It in itself doesn't mean anything.
You Prove Yourself by doing Good Sumou.
Good Sumou must be: 1. Power Sumou 2. Offensive Sumou 3. Basic Sumou 4. Spirited Sumou 5. Speed Sumou 6. Pauseless Sumou 7. Tenacious Sumou
To do Good Sumou in Shoubu you physically need: 1. Power 2. Katachi
This is the Tai aspect of Shin Gi Tai. All round, to do Good Sumou, you must embody Shin Gi Tai.
The opposite of Good Sumou is Bad Sumou. This is the worst thing a Rikishi can do.
Good Sumou going with all Power is reflected in Aun no chikarawaza, one of Sumou Sayings.
Doing Good Sumou means doing Your Sumou all the time and nothing else.