It's important to be able to understand the people who manage and own a prospect company, in order to help understand potential decision makers, and the potential opportunity size through connected companies.
The Summary shows the company's position in it's group, and the number of directorships, shareholders, portfolio companies and related companies associated with the company.
The Beneficial Owners and Shareholders are listed to help illustrate who has a financial interest in the company.
The Parent and Portfolio companies sections can be an extremely useful tool in helping you to maximise the size of the opportunity you're working. For example, one user was able to significantly increase the size of the deal they were working on by identifying that the company they were speaking to was a subsidiary in a larger group of companies. Using the Group tab, they quickly identified the ultimate parent, approached them, and made a sale across the whole group.
A similar principle applies to the Related companies section - these are companies which might not be related in terms of share ownership, but where there are similarities that could indicate you could extend your relationship to them too.