Is it important that the reality of things doesn't exist, instead of just behaving like things don't exist?

In some traditions their philosophy says that concrete things don't really exist, only in the mind like just an experience. But is that vision important, or could just your relation to those things as if they don't exist be enough? In other words, is this philosophy just a way to concentrate on the spirit, instead of the outer world, or do they really mean this?