Step width and peak knee forces.

Forget older adults, this is for everyone. If you have a step width that affords knee over foot, hip over knee, and you load those stacked joints, there will be less peak adduction and abduction loads at the knees . . . . and less risk for frontal plane drift of the hip-pelvis, improved control of limb rotation during loading, and reduced risks for over pronation at the foot-ankle complex. These are anti-cross over gait principles.
And, this is obviously not just a stair descent or ascent issue, these are normal fundamental gait (walk and run) principles that just make good common sense !

Knee. 2014 Aug;21(4):821-6. doi: 10.1016/j.knee.2014.03.006. Epub 2014 Apr 3.

Effects of increased step width on frontal plane knee biomechanics in healthy older adults during stair descent.

Paquette MR1, Zhang S2, Milner CE3, Fairbrother JT2, Reinbolt JA4.