For 40 years I've used aperture priority as the basis for my exposures. Now, as I do more street photography I'm finding it convenient to let the camera decide both settings - it's faster and I can concentrate more on the subject and less on the camera settings. That works for maybe 70% of the photographs I take, but when I do want to change a setting, it's almost always the aperture I want to change and I usually want it to be smaller.
On my Pentax K5 I notice that given the same scene the program settings deliver smaller apertures (and slower shutter speeds) by default. A friend who uses Canons tells me the same thing, compared to his X-T2.
Program shift may not make sense to you, but for my purposes it does make sense for me.