Twybil

[Toolmaker51]

As usual, Wikipedia to the rescue. I enjoy researching unknown tools and processes. Of the entire page, the following copy/ paste is my favorite. It illustrates an untold number of situations, and probably why we enjoy what we do...I've added emphasis in bold, along with a slight change to the paragraph structure. It may have been written concerning the twybil, but ANY instrument could be inserted without altering 'the message' found there.

In the heyday of the twybil, mortises in small work were often round-ended and so could be cut very quickly by brace and twybil alone, the tenon being rounded to fit.[9] Only large, or high-quality work required the square ends and smoothed sides of a precise mortise, trimmed by this variety of chisels.
The apprentice will often use all three mortising tools interchangeably and randomly, making much effort of removing the waste as small chips.
The skilled framer uses each appropriately in turn, working faster, with less effort and not bothering to tear a large block of waste into fragments. They are also less likely to damage a precise edge by levering with a sharp, brittle chisel edge.