The concept of algebra is to study the rules of operations and relations. So it matters what X is because it shows a relationship and how two equations are related to each other. It is a sort of abstract way of showing relationships between concepts. There are many correlations and relationships and parallels in the world, and those can be shown through the application of algebra. It is largely helpful when you need to analyze various forms of data.
[OOC: For the record, I have no clue what I just typed. I am just going to merely nod and not try to understand.]