What you see depends on where you are standing
The size of the wave depends on where the person is standing. This activity helps us to appreciate that people have different kinds of knowledge from different viewpoints.
What practical use is this in real situations?
When you are working with other people they are not not necessarily going to see things the way you do. And arguing is probably not going to shift their position. If you want to work with them, or get them to do what you want them to do, it is much more effective to think what argument would make sense to them in their present position (that is, from where they are standing).
Frame your argument this way — you are more likely to be successful.