Oversaturated work markets are bad in all regards.
Wages get reduced... So does work stability, promotions, mentoring, work hours, work based benefits.. hell, the lack of qualified personnel in a country can be directly linked to companies no longer educating their staff for said positions and just expecting everyone to have them before being hired..
Companies have no particular motivation to develop staff or provide positive working conditions or guaranteed employment when someone can always be theoretically available to fulfil the role at any point.
Of course that leads to bigger issues with housing affordability , but that's another issue... That mass immigration effects negatively aswell...