["Journal of Management Studies, Volume 63, Issue 6, Page 2608-2645, September 2026. ", "\nAbstract\nThe rise of digital labour platforms has made side‐hustles a defining feature of modern work. The debate over whether side‐hustles benefit or burden full‐time work remains unresolved. We propose side‐hustle thriving as a key factor. Drawing on the conservation of resources theory, we theorize dual pathways: Side‐hustle thriving enhances full‐time work performance through psychological detachment from and affective well‐being within employees' full‐time roles (resource gain), yet simultaneously impairs it via side‐hustle attention residue and full‐time work resource depletion (resource depletion). Two studies, one with 10‐day experience sampling (N = 97, 644 observations) and another with a multisource, multiwave design (N = 247), support this framework. Crucially, we identify boundary segmentation preference between side‐hustles and full‐time work as a key moderator: Employees who strongly separate work domains amplify the resource gain pathway while mitigating resource depletion. This research offers a nuanced framework for managing multiple jobholding in the gig economy era.\n"]