Set Square wrote:

It's amazing what you learn here! In my 45 years of DIY, I'd never heard of
a scutch chisel until today!

Is the idea that, with its serrated end, it will dig in and allow small
quantities of material to be removed in a controllable fashion - whereas a
plain chisel would glance off?

Exactly that. I'd never heard of them either till quite recently; it
was a joiner watching my efforts at forming a doorway in a brick wall
who put me onto them. The combs themselves are disposable and fit in
either chisels or directly into hammers; personally I prefer the chisels.

David