Libertarians of all stripes generally agree about how an ideal world would function, and so the reasons libertarians have for arriving at that conclusion wouldn't matter much in such a world.
But in the actual world, where libertarian principles are forced into conflict against each other, the ideology by which a libertarian prioritises her principles is just as important as the principles themselves. Maybe more so.
Two hypothetical libertarians each say they support immigrant rights in an ideal world. But one of them supports immigrant rights in an imperfect world and the other says that preventing a larger welfare state justifies junking immigrant rights. Well how did they decide that?
What philosophy told them how to organise their libertarianism that way?
Another common example: two hypothetical libertarians each say they'd oppose the forced redistribution of wealth in an ideal world. But one of them says centuries of institutional violence directed at certain communities, which hopelessly mal-distributed economic, political, and social capital, require us to rethink our distribution principles, while the other libertarian says "well that sucks, but two wrongs don't make a right."
Again, what philosophy is doing the work of determining which camp you fall into?
Libertarians need to figure out "how our principles can degrade elegantly" in the face of historical atrocities that forever taint our idealism, which I've never forgotten.
So I guess my thesis here is that libertarianism is starting to seem more and more like an at least partially empty vessel to me. It's a language, a way of talking about human rights and ideal forms of government. It's a set of principles too, but not a self-defining one.
In an imperfect world, libertarianism requires some other philosophy in order to orient itself, to define the terms, and to help reconcile the conflicts in the application of ideal principles to a decidedly non-ideal world.
And lastly, I'll suggest that two libertarians who use wildly irreconcilable philosophies to organise their libertarianism are often further apart from each other than either is with non-libertarians of a similar background bent.