If you're trying to decide between inviting a user as a member or as a guest to your workspace, the key thing to know is that members have more options and control over their Height experience than guests do.
Guests are able to collaborate on tasks, projects, views, and lists, that they have access to. This means that they can make comments, mark tasks as done, and create new tasks within lists they have access to.
Things guests can do:
Guests can only see and discover tasks, projects, views, and lists that they have been added to by email / name.
Guests can be added to views, but they'll only be able to see tasks that have been shared with them. Tasks in the view that have not been manually shared with the guest will be hidden from them.
Guests can change the view settings (e.g. Section by, etc.) for views and lists they have access to, but they cannot save the changes.
Guests can use filters on view and lists they have access to, but they cannot save those filters as a new view.
When first invited to the workspace, guests only know about (i.e. can see the name / avatar in places like "Assignees" or @mentions) of the user who invited them to the workspace. (Once other users interact with the guest on a shared object, they'll be able to see that user's name across the workspace.)
Within Settings, guests can only see and make changes to Personal settings like Notifications, Profile, and Preferences.
Things guests cannot do:
Guests cannot be added as members of a team.
Guests cannot see any team's tasks, projects, views, or lists, unless they have been manually invited to the specific object.
Guests cannot use the Share menu to add any other users to tasks, projects, views, or lists.
Guests cannot invite new users to join the workspace.
Guests cannot use the search feature.