The idea is to update the existing text in the front display text window instead of displaying the text in a new window.
This feature might be useful for cases when it is required to gather information from different apps or tabs and display summary of the gathered information in real time in a single text window.
This is unlikely to happen.
Use a Custom HTML Prompt action is you want more control over a persistent window.
I use BBEdit when I want a dynamic text display environment, because it's one of the most AppleScriptable apps out there.
Even the FREE (Lite) version it becomes after the Pro version's demo expires.
The one drawback it has is that it's plain-text only, although that's usually sufficient for my needs.
-Chris