For my yoga business, the audience report in Google Analytics would be useful to know the age and gender of customers clicking on the website as well new versus returning customers. It also tells you where your customers are coming from geographically. Having this information can tell you if you are reaching your target market and if you need to change your advertising approach. It can also help you identify new audience targeting opportunities.
The Acquisition Report informs you how people are finding your website. Is it organic, meaning they typed in some keywords and your website popped up or is it direct traffic where they are familiar with your website? It might also be a paid search as in Google AdWords or they might be linking from social media. This information is useful in deciding what is helping potential customers find you.
The Behavior Report lets you know what people do once they reach your site. How long do they stay and which pages do they find more compelling than others? It can also let you know what day and time of day they visit most often so you can schedule your changes or new information based on that. Perhaps you need to add more compelling or interesting content to keep their interest.
You can also add custom settings if you want to track very specific details about your customers. There is so much information you can track but first, you need to know why and what you will do with the information.