Someone always asks this, and it's been answered many times before. In short: this specific result probably has no practical applications just now. But there

Someone always asks this, and it's been answered many times before. In short: this specific result probably has no practical applications just now. But there are several points to consider: 0: The techniques developed to answer the question might be useful for other applications; 1: It can be fun to chase down problems like this; 2: Sometimes results like this end up being useful decades, even centuries later; 3: The skills the researchers develop might be able to be used on other problems; 4: Not everything has to be useful. Consider music, art, hobbies. As examples of some of these: a: Elliptic curves were initially studied purely out of curiosity. Now they form the basis of modern cryptosystems; b: Factorising Integers was regarded as the pursuit of cranks, until it became an important tool in breaking cryptosystems; c: Latin Squares and Lattices were studied well before they were suggested as a possibility for post-quantum cryptography; d: Graph Theory was chased purely because it was interesting, and now forms the foundation of a gazillion algorithms; e: Eigenvectors were studied purely out of curiosity, then suddenly they became the basis of the Page Rank algorithm; f: Non-Euclidean Geometry was created purely to show that classic geometry was probably right, then showed it was actually "wrong", then turned out to be useful in relativity. And so on. There are more, and thousands, possibly millions of words have been written on the subject of how pure research, pursued simply because it was interesting, has turned out (in some cases!) to be useful. The 9th Dedekind number is unlikely to be useful, but its pursuit may be valuable in ways we can't imagine.