It does keep wages down on a lot of blue collar manual labor jobs. That's about it, but that does happen with a certainty. I used to work new construction housing. Framers, drywallers, cement layers, and roofers etc either work for less money, or end up not working because the company with Mexican laborors making $5+ an hour less underbids everyone else and the "builder" subcontracts out to that operation.

It's why so many of those laborors don't want immigrants. They see it directly effecting them, while so many others are completely ok with immigrants. It doesn't effect most other people's paycheck and it doesn't raise prices of anything they buy.