GS1 Product Image Specification 3.3.4 still asks for a clipping path "within one pixel". Below, the same three product photos are cut out twice: by a vector path traced from the mask, and by the alpha channel itself. Move the sliders and watch what each one costs.
Where in the soft edge the line sits. Low keeps the fringe and its background; high cuts into the product.
How far the Bézier curves may stray from the mask edge. The standard allows 1 px.
Print RIPs and DTP tools choke on huge paths. If the budget is exceeded, the tolerance is loosened until the path fits.
Steepens the alpha channel itself. 1 is the computed matte as is; higher values push soft pixels towards solid or clear, until alpha becomes as hard as a path.
On a machined part the path follows the mask within half a pixel using a few hundred anchors. Here the path is redundant, not wrong. It is the alpha with the antialiasing thrown away.
Every thin sprig adds anchors if the path is to stay within one pixel. Cap the node count and the curve starts cutting corners. There is no setting that gives both.
A hair is partly transparent across several pixels. Any threshold either keeps a halo of the old background or shaves the fur off. Alpha stores the true coverage and composites cleanly on any colour.