There several good reasons why you might want to add computer control to a layout.

ComputerDCC group members want to watch trains running round the layout in a prototypical way which allows them to do other things. This might include work at a station, in a yard, or at an engine depot.

Computer control allows operators to run trains automatically and manually at the same time (i.e. it adds virtual operators without having to provide space and equipment that real operators would need).

It adds a huge sense of realism to the way you run your layout.

It can greatly enhance the operation of club and exhibition layout, enabling operators to share more time with their colleagues and visitors.