[MrB]

When you're on Aperture priority, and use the widest all the time, you're most likely assured of the fastest shutter speed given the any luminance. This is assuming I'm not after long exposures.

Although a shutter speed fast enough to avoid the softening effect of camera shake is important, for me the purpose of Aperture Priority Mode is the control of depth of field. With a modern camera and lens, the combination of their image stabilisation and higher ISO capabilities usually enable much greater than adequate shutter speeds, even when using quite small apertures to maximise depth of field.

Cheers.
Philip