[Retra]

Under any practical consideration, free will is nothing more than an emotion; it offers you no capabilities, only a propensity to respond to things in a certain way. Without a useful definition of free will that offers something different to this, you won't have a key to anything.

[colordrops]

Why it has to be useful? We try to understand countless things without have a use case in mind at the time of study.

[Retra]

So you're fine with a key that doesn't open anything? How will you know it is a key at all then?

>We try to understand countless things without have a use case in mind at the time of study.

You're making a pretty clear reference to mathematics & science here, but in those disciplines we study things with well-defined structures. We don't study flighty nonsense because it's not ever going to be useful. You shouldn't invoke this phrase to excuse a lack of precision and clarity.