What exactly is the question? Do you mean the advantages and disadvantages of having a player on the national team?
If so, no disadvantages that I can think of (other than the fact that maybe others in your country will be able to see the skills of your player). Advantages include helping your national team compete in the world, and also a merchandise boost (extra income).
Just to clarify, playing in NT games has no effect on game shape and/or injuries right? In other words, it's not possible to overwork a NT player unless through your own doing in league/scrimmages and he won't suffer any injuries playing for the NT?