Advantage and disadvantage of immigration law?
I'll assume you mean immigration reform, as in changing the current law. The main advantage of doing so at this point is that we could address some of the most glaring flaws in the present immigration system, which most people would agree is broken and dysfunctional. We could adopt a sensible, humane and secure way of allowing guest workers to enter the country and reside here in the open, or adopt a more realistic path to citizenship for the immigrants already here.
Some disadvantages would be that such a debate over a reform law would divide the country even more so than it is now (which is saying something), and we would hear more open racism against immigrants, and rather than using the topic as a real and crucial subject for debate, politicians will undoubtedly seize the topic to inflame voter passions and use them to get re-elected.
It would help if you could tell us what aspect of immigration law you want us to discuss.
To me, one of the major problems with our immigration law is that it places an emphasis on families. It is much easier to get into the US if you have family members already there. This means that we approve immigrants based on who they are related to rather than on how much they can help our country. I think it would make more sense to bring in immigrants who have particular skills that would benefit our society -- skills that we do not have enough of in our native-born population.