Is the exact value of any likelihood meaningless? While reading about likelihood, I have heard that "the exact value of any likelihood is meaningless" why?
So, because of that we may use the likelihood ratio.
So, my question is, why the exact value of likelihood is meaningless? And what is the benefit of likelihood-ratio over the likelihood?

It's “meaningless” in the sense that it's very hard to interpret, it's just “the bigger, the better”. That is the case because the likelihood is not probability and it is calculated without normalizing the constant so the numerical value can be any non-negative number. You still can maximize the likelihood because lack of normalization doesn't matter for optimization. See other questions tagged as likelihood for more details like What is the reason that a likelihood function is not a pdf? or What is the difference between "likelihood" and "probability"?.
