[eximius]

If you work in a big company making internal web apps for HR to manage payroll, then no, the lambda calculus will never be useful to you.

However, if you want to do research, it is an invaluable model of how computation works. It's simplicity allows for reasoning about complex ideas while minimizing the cognitive overhead of the model.

It may also help you understand why certain functional styles behave the way they do or how to better implement programming languages.

If none of those things interest you, then yes, it is not useful. But a large crowd here IS interested in computer science theory and programming language theory and functional programming so they are interested.

As a final analogy, you might consider this the 'Standard Model' of computation much like there is the Standard Model in particle physics. If you are a civil engineer, it will never be useful. If you are a chemist, it might be useful only in passing. But if you are the physicist, it is invaluable.