Immigration is not the best method to help those from economically disadvantaged countries. A job created in said country could end up helping multiples more people that importing just one person. It's better to spend the money that would otherwise be invested in immigration into foreign investment and charitable activities instead. It's also impossible to accept an unlimited number of immigrations (say all the immigrants from the Middle East that want to come to Europe now) and eventually people will need to be turned away, and consequently significant number of immigrants can dilute the host nation's jobs market and cause hardship for the host nation's citizens/residents.
But immigration is also an important method to help get talent and ideas to where they need to be. Often countries lack a certain skill set and have a surplus of another skill set, so exchanging immigrants can be a way to help get everyone jobs and turn ideas into reality, though in the current times it is also achievable through the internet.
A big difference between immigration from developing countries and developed countries is that the latter tends to have more muted immigration allowing for more liberal open borders (say between Canada and the US, or between Ireland and the UK).