When you set a person as "owner" of a task you delegate him/her the power to update the task. He/She will find this task in "My work " and in that screen he/she can directly update: the percentage of completion, the status, the indicator or add comments.
When you allocate a resource to a task, you assign man.days on a given duration. By doing so you authorize the person to track actuals in his/her timesheet on the line corresponding to this task. A link in the screen "My work " enables them to directly add the task to the timesheet. Assigning resources to tasks allows you to manage the team’s workload. The resource view will then display total workload and every resource’s capacity.
A person can be “owner” and/or “resource” depending on what you want to achieve.