Transient covert attention increases contrast sensitivity at the target location with an informative spatial cue. Here we explored whether an uninformative spatial cue (50% valid with two possible locations) also increases contrast sensitivity and whether contrast sensitivity is altered at the uncued location as compared to the neutral condition. For all four observers, transient covert attention had both a benefit and a cost: it enhanced contrast sensitivity at the cued location and impaired contrast sensitivity at the uncued location at both parafoveal and peripheral positions. These results are consistent with the idea of limited resources, and indicate that transient attention helps control the expenditure of cortical computation.