It could increases the size of the economy longer term but makes the average poorer. If there is an area of the economy with worker shortages it could increase

It could increases the size of the economy longer term but makes the average poorer. If there is an area of the economy with worker shortages it could increase production. But add immigration to a balanced job market and wages drop, employer profit increases (rich get richer) and the economy grows. Replacing workers with slaves increases the economy. Canada has encouraged mass migration and it has kept wages extremely low and has also increased the price of housing.