Job autonomy is regarded as a resource that enhances motivation and performance. Yet, scholars have begun to question its uniformly positive portrayal, suggesting that job autonomy may have downsides. Addressing this debate, we examine how job autonomy can simultaneously foster desirable and undesirable outcomes for employees. Drawing from boundary theory, we propose that job autonomy increases problem‐solving pondering, which enhances task performance but impairs psychological detachment. Our findings from a three‐wave, time‐lagged, multi‐source study ( N = 331) were consistent with our predictions. For long‐term well‐being, it may be especially important to support high job autonomy employees in managing work–home boundaries that enable them to disconnect and leave work problems at work.