It's a difficult topic: there is something to say for both major points of view. Heck, there could be even 3 or 4 major points of view if we tried. But for now there are 2: no benefits and the total package of benefits and risks.
Let me start by saying this: It somehow just doesn't feel right to let your best players play for the glory of their country without getting anything in return (just a little xp at the most), or even having a say about it... The reward should be the full package: Xp, training minutes, a salary refund, the choise to refuse your player to play for the NT AND the risk of injuries.
Or does it? All of these benefits sound nice if you are training 1 guy for your own NT somewhere in division II or III and can barely pay his salary, but who are going to benefit from this package the most? Right: the people owning multiple NT players, and there is a tournament with simular benefits set up just for them: B3! Don't get me wrong: they deserve it, because they ARE BuzzerBeater's Best (and richest) but is it fair to give them even more? And even worse: as they are earning more and more money they will be able to pay the ridiculous prices asked for NT players and the same prices (and high salaries) will tempt more lower division NT player owners to sell theirs...
On the other hand, can a NT coach expect a team owner to keep training his star NT player to extreme levels on the mayor skills, and give nothing in return exept bragging rights? Salaries are sky rocketing (although I don't believe we will be seeing 150k salaries in the near future) and they will back fire on the transfer prices (already/soon?). So what's the use to keep training them for the NT?
I guess we will just have to do with the system as it is right now: in a couple of seasons todays trainable NT stars will have become 25yo untrainable NT powerhouses who mostly will be owned by the top teams in BuzzerBeater, taking away the need to finacially compensate their owners (being the best doesn't come for free!!) for letting them play in the NT as long as those games won't have a negative effect (injuries and so) together with a (if any) slight effect on the experience of the player... But that's just my opinion :)