How are undocumented workers helpful to the US?

There is a lot said about how undocumented workers are doing damage to the US or causing some disadvantage or negative occurrences. They are not all negative when you take into account a lot of food that we eat, we would not be eating or getting as cheap if the undocumented worker were not doing that labor. Back during the housing boom, I am sure many of those homes would not have been built or would have cost more if undocumented workers did not have their hands in it in certain areas and housing markets. Have you seen, 1st hand, or through work, where undocumented workers were helpful, or served as a plus being here in the US?