People worry that automation will drastically affect wages for those humans who manage to keep their jobs, and that's fair: it took more than 1.5 centuries for workers' wages to recover after the Industrial Revolution, per The Economist.
The introduction of machines and tools created a significant demand for unskilled labor (it rose from 20% of the workforce to 39% from 1700 to 1850). Machines either pushed craftsmen out of the labor market completely, or encouraged employers to decrease their workers' wages. The Economist cites this exact situation in which wages fell drastically in the early 1800s, not recovering until 1960.
Why it matters: That's a long time for wages to recover, and machines have become increasingly advanced since 1960. Most of them, at least in some industries like manufacturing, are introduced to eliminate the need for workers or, ultimately, they alter the way employers think about workers' wages in an age where cost-effective and time-saving machines are becoming ubiquitous.