The Steve Miller Band are famously pickers, grinner, lovers, sinners, jokes, smokers, and midnight tokers. So if you were to target The Steve Miller Band in your marketing, you would inevitably end up targeting a wide range of people. The Venn Diagrams of Steve Miller Band overlap with a variety of interests.
This handles the objection of “won’t it limit who we target.” But it doesn’t explain why we do it in the first place. And the best answer I can give you there is authenticity through specificity.
Your audience can tell when you’re pandering. Your copy will be vague, and while it will apply to your audience, your audience won’t buy what you’re saying. Remember, the audience can smell authenticity. The best way to be authentic is to speak the same way your audience does, and the best way to do that is to be specific. People relate to specifics. People see themselves in specifics. People are individuals; they are not vague notions.
Hopefully, this clarifies why you want to be specific and detailed when you strategize about your ideal customer.