Providing feedback on the overall quality of a users prompt allows them to adjust it in real time before submitting for generation.
Both novice & experienced user can benefit from instant feedback on their prompt.
Any generation be it either image or text takes time, so allowing users to author quality prompts faster.
Depending on your context what determines a prompts quality could vary across multiple dimensions. For example length, detail, specificity or context description.
Consider providing feedback on multiple dimensions if it empowers users.