Variation
Because of its natural source, leather has slight variations in thickness, texture, surface markings, colour... within a single piece.
This is exactly what appeals to many of us who love the material - along with its wear properties, longevity, touch...
Each item made is unique
I match the hides that I buy to each design - all are different from one another.
I cut from parts of the hide according to its intended use. I will include, for instance, sections with surface scars if I think that that will enhance the finished article.
(See 'Wildlife' side-panel)
(Also see 'Rugged' example).
The dyeing process also brings its own variations. Perhaps you would only notice such differences on close-up inspection across, say, an all-black item, but each 'sunburst'-type finish is a one-off.
.
.
Wildlife
For special purposes, I'll sometimes use a hide from an animal that has had a rather more wild life than, say, most British herd cows have had.
This can produce a nicely rugged-looking finish.