Needles designed for sewing thick canvas or heavy leather (e.g. on a traditional sailing ship) have a triangular point, see example 1 and example 2. (These needles are sometimes also called “rigging needles”, but then again not every “rigging needle” is three-edged.)
Leather: Also known as glovers and as wedge needles, these have a triangular point designed to pierce leather without tearing it; often used on leather-like materials such as vinyl and plastic.
Sailmaker: Similar to leather needles, but the triangular point extends further up the shaft; designed for sewing thick canvas or heavy leather.
The only stated reason I have found is that this design supposedly allows the material to be pierced “without tearing it”.
How would the design of the needle prevent tearing of the material? Is this the (main) reason that needles designed for sewing thick canvas or heavy leather are three-edged?
(Side note: apparently three-edged needles are also used in acupuncture.)