The App Store Optimization (ASO) Indicator gives you direct feedback while editing your metadata within App Manager. It shows the ASO "value" for each field as a colored progress bar.
We regularly crawl the top 400 apps on the App Store to get our reference data and give you a meaningful cue, if you should add more text.
As there is no right or wrong on the App Store, we only want to show you a "trend".
Red means "low", add more text/characters; especially useful for keywords and description
Yellow means "okay", but a little bit more text might be even better!
Green means "great", you're in the average character count of the top apps!
Great that you ask! The importance of the ASO indicator varies by field.
App Name: keep it short and simple, so it gets displayed on all devices without getting cropped!
Sub Title (iOS 11+): same rule applies as for the app name
Promotional Text (iOS 11+): not really significant (yet)
Description: One of the main reasons for us to introduce this small feature, was to get a better feeling, how much text is needed for the description. "Getting" to green is usually a good sign, but after that, it's questionable if you need more word (or if your users will read them!)
What's New in this Version (Release Notes): Philosophies vary on this topic. From what we've seen keeping it short and meaningful (!) plays out very well in the long run
Keywords: Maybe the "most important" field on iOS except the app name. You always want to use all 100 characters to give you app the biggest possible exposure!