Sometimes, things take more than a simple reply to resolve. Sometimes you need to task a team member to solve a problem, create content, or circle back with the one person who knows how that software system you wish you could leave in the dark ages works.
That's what the tasks interface is for - Not only does it let you see all of your outstanding tasks, it lets the agency owner get a top down view of what tasks are still outstanding, or even late, right from the agency dashboard.
Tasks are one of the most effective ways to remember to knock out those requests to completion - even if they take several days of back and forth from your team internally!