If you spent a lot of time and money moving to a new country for work then you don't want to do all that again. In the USA, if you aren't a citizen and you have a working TN visa, then you literally have DAYS to find a new job or else you get deported. Thats why its important, because the current laws aren't realistic with finding a new job. They don't take into account the multiple interviews, the slow responses and callbacks. The entire process takes a long time.