For an example, if your Puritan ancestor came to America on the Arbella, and their profile is labelled "Category:Arbella, Winthrop Fleet", then the link will take you to a page listing everyone who came on the Arbella, with their names linked to their profiles. It is likely that people related to your ancestor will be among those other profiles.
Categorization is not only used on WikiTree, the concept has been around for ages. Here is a Wikipedia article about it. On WikiTree, categorization may be used to add data once which may then be applied to all the profiles included in the category. For example, if your ancestor was in the Indian/Colonial conflict known as King Philip's War, you would add the category to their profile. It would connect to a page with the details of King Philip's War, and a list of people involved, linked to their profiles. I have been adding the categories of Puritan Great Migration, 1776, King Philip's war, Magna Carta, and others for months.
Today I realized I need to work at understanding how to create categories so I joined the Categorization Project. As a bonus, I have a new badge:
February and March were both productive months, as you can see by my Club 1,000 badges.