How is Hillary wrong, Part 2

On her website, Hillary Clinton says that comprehensive immigration reform will "bring millions of hardworking people into the formal economy". What are some of the downsides of doing that, both the obvious ones and hidden ones? I realize you have many disagreements with Hillary, but I'd only like you to address that one promise she's making. Please tell us what are the downsides of her specific promise. Would you like me to read it again, before you comment on her specific promise?

Supporting information: 

Quote from hillaryclinton . com/issues/immigration-reform

The desired answer is for Trump to show that he's thought about this issue enough to be able to figure out this argument. Obviously that's not going to happen.