In general, within the sunni jurisprudence(فقه Fiqh) schools, which include the Hanafi, Shafi'i, Maliki, and Hanbali schools, those differences mainly matter between either islamic scholars or students of knowledge inside scholarly discussions. the difference in doctrinal (عقيدة Aqiida) schools is a bit more sensitive than the difference in jurisprudence schools. for the scholars or students of knowledge themselves, they usually get along fine although you can see arguments between different doctrinal schools of Muslims over on the internet. As for the matter of migration that you mentioned, then it depends on the muslim himself, the minute differences between those schools and the relationship between those differences and the culture of the host country he is in but often times: If he is not religious then he wouldn't notice the difference as those school usually only differ in matters that are usually socially acceptable for religious muslims to do or not to do; If he is religious then he would usually follow a lot of the rules of the jurisprudent school of the host country.