I always try to manage national teams at some point. You're not a true legend of the game until you've got a world cup on your cv. It is pretty hectic but its worth it for forming good relationships with players outwith your club. It may make certain players easier to sign. Also, if you happen to have important players who you manage for club and country at the same time, you can pick them appropriately so they don't get injured before an important game.