You can use the search results in many ways, and not only on Reddit. For example, you can find low competition keywords that you can target directly: without a tool like this, it'll be impossible to discover such a thing. Second, you can use the results to understand your audience or to find it. Keywords are just a surface, but they are also an important hint about what a community is more passionate about, what are they most interested in, what are they discussing in a given moment in particular... All this information is vital to customize your content so that it responds to your audience's needs.