Every decision in this course — what to write, which platform to use, what an ad should say — depends on knowing who you are talking to. Get this wrong and everything downstream is guesswork dressed up as strategy.
The instinct is to keep the audience broad so as not to exclude anyone. In practice, messaging written for everyone speaks to no one — it has to stay so general that it stops being useful to any particular person.
A page saying "we provide quality computer services for all your needs" gives a reader nothing to recognise themselves in. "We recover data from water-damaged laptops, usually within 48 hours" is narrower and far more effective, because the person with a water-damaged laptop knows immediately that it is about them.
Most audience descriptions are invented at a desk. The useful ones come from evidence you already have access to:
A useful audience description is short and decision-shaped. For each group you serve:
Personas earn their keep or they do not
Detailed personas with invented names, ages, and stock photos are popular and frequently useless. A persona is only worth having if it changes a decision. If your marketing would be identical with or without it, the document is decoration.
Most businesses serve several distinct groups with different problems. A computer training institute might serve students choosing a first course, working professionals adding a skill, and employers looking for trained staff. Those three want different things and would not respond to the same page.
The answer is not one message that covers all three — it is separate pages, each written for one of them. This is the same principle as the SEO course's "one page, one topic", arriving from a different direction.
Audiences change. The problem people came to you with three years ago may have been solved by something else, or replaced by a different one. Re-reading your own enquiry messages once or twice a year catches drift that is invisible day to day.