The clip is used when I want the extra reach that blade offers or I'm cutting *food.
The sheepsfoot is reground to the thinnest angle I can get the blade at with the edge not failing under normal use. The short blade length and nice point make this an excellent precision blade IMO. I bring the edge to a high, hair whittling sharp polish and reserve it for when a high degree of sharpness is desired.
The spey is ground slightly thicker, but still no more than 10 degrees per side max. This is my general use blade for things like opening packages, cutting cardboard and other mundane chores. I chose this role for the blade because I don't want to wear down the tip of the sheepsfoot too quickly, the spey has a solid snap to the back spring, the curved handle gives this blade great ergonomics and I never really had a specific use for this blade so it became the general purpose blade for me.
*Sometimes I use the sheepsfoot for food. I'll use the clip for cutting up meat or an apple, but if I'm cooking pasta and just slicing some onions into the pot or want to peel a carrot, I go with the sheepsfoot. Sharper and thinner is always better IMO.