I'm unconvinced it's a "net benefit". Fundamentally, what we have is a movement of time use from higher-valued to lower-valued. I would have individuals who volunteer to serve pay the cost (by using vacation time) so that employers (and ultimately customers and taxpayers) aren't paying the cost. Trying to argue "net benefit" is difficult to impossible and isn't really the tack to take.
Big picture, I'm also unconvinced the cost of the Res F has been worth what it has provided in Reg F augmentation for the past 40 years, going back to and beyond the old "flyover" billets for fall ex in Germany. I've heard the "invaluable, critical" assessments all through FRY and Afghanistan, but I doubt any of the assessors were thinking in terms of Bastiat's seen/unseen. One of the alternatives to the funded, not-very-employable Res F we have is a more-funded Reg F. And then would the Res F still be needed for anything short of "total war"?
I've always been emotionally sympathetic to the "net benefit" view, but not intellectually. I've not seen anyone crunch numbers to "prove" these propositions one way or the other. But the high-to-low value use of time is undeniable.
Military leave provisions in law for everyone might be a necessary component of re-working the Res F to be more valuable. That can be true, and it can also be true that it's a net cost. As I perpetually write, mobilization of resources is inefficient. Make the case for the necessity, but mostly* don't try to argue that any costs are saved.
*The significant exceptional principle: a military force that successfully deters conflict is cheaper than one that does not.