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.
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.
Which means that we should act as if we have free will, since no other approach is reasonable given our perspective.
Interesting to note that the Bible implies something like this paradigm, since it describes God as having total control of the universe but also says we have free will.
When you first encounter that pair of ideas in the text they seem contradictory, but further reflection eventually leads many to some variation on this idea.
I don't believe it's the full picture of free will and predestination in Christian theology - just think it's interesting that it fits with this perspective that would have been quite non-obvious to its authors (at least in regards its relationship to modern physics).
