Bursty highly intensive usage.
Photography might be an example where you're not hammering the CPU all the time (unless doing batch updates) but when you want it to work you want it to work fast (tweaking a photo, HDRing etc). Those tasks are not constant though.
Video might the opposite, where you are doing a large video "task" and it's going to thermally throttle anyway, in which case it might not make much difference (% of time taken by the task).
And I know both of these cases may be using the GPU and the CPU, or the GPU, or the CPU, but I think the principle still applies, even if the specific examples can be called into question based on the specific software being used for the task.
Short and bursty vs long and sustained is the key. Coding might be a good example too - you're not always compiling, you're only doing compile tasks at intervals.
EDIT: I should add, I'm assuming that there is not the capability for unlimited extended bursting.
