arXiv:2610.41196v1 Announce Type: new Abstract: Large flexible loads such as data centers can shift consumption across locations and hours to lower their bills. We model a price-making consumer leading the system operator in a Stackelberg game and compare its shifts with a cost-minimizing planner's over a simulated RTS-GMLC year. Strategic temporal and spatial shifting capture 75% and 93% of the planner's savings, forgoing the rest mostly by withholding flexibility to protect favorable prices. Scarce capacity and abundant renewables raise this share for temporal shifting; scarce transmission lowers it for spatial shifting. Temporal and spatial flexibility substitute for thermal and transmission capacity, respectively, and complement renewables.