Topic properties are important parameters of a topic in a more structured way. All properties are optional.
You have a topic on a project that needs to be finished by the 25th of March, and which should be worked on by John Doe.
You could, of course, state in the text of the topic description who is the assignee and when is the deadline. However, by setting topic properties:
assigned: John Doe
You can set this information and make it available for your whole team in a more formal and readable way.
It also allows you to set handy automation to save you manual time.
For example, when you assign a team member to a topic, he will be notified by email. If you have no time to see them anytime soon, they will at least be notified of the work to be done and not waste time on other priorities!
Deadline: Deadline is the expected date when the topic should be finished.
Assigned user: This property allows a topic to be assigned to a user who will then be invited to work on the project. You also could assign yourself, of course!
Sprint: Sprints are special dates when a set of tasks need to be terminated. It could be used for example to group topics for the next meeting.
Stage: Stage is a broader step of project development commonly used in architecture projects. Usually, architecture projects are broken down into sketches, preliminary design, design, and site work. Defining a stage, which a topic belongs allows you to archive all topics of a past stage or access topics that are planned for a future stage in a separate view.
Priority: Prioritizing urgent over less important things is the key to survive in a busy and stressful workflow of project development. Urgent topics will be highlighted to remind people in your team to handle them first.
Package: Package is a common way to split the work that needs to be done by construction types: walls, facades, interior finishing are possible values of a package. Depending on the projects you could split them into very specific packages or use only generic separation. Package is a way to prepare site work and give access to external uses. For example, the construction company can have access only to the topics that are about their specific package.
I hope you find the topic properties useful. You are not obliged to use all of them. Just test those that are useful for you.