First of all, yes, I know that 0.01pt is already microscopic (that's what, a third of the finest stroke one can put down with a Linotronic?). Wanting 0.001pt is just insane except for an admittedly fringe but likely growing (and rapidly growing at that) use-case.
The software which drives many popular laser cutters (Epilog, Trotec) as well as other types of cutters uses vector data for etching and cutting materials. What they all seem to have in common is the special use-case for data which will actually be laid down as vectors eg by moving the laser in two dimensions to make continuous curves as opposed to scanning back and forth to etch a raster (or rasterized) image.
The software will not recognize a cut (or a vector-based engraving) unless it is set to: 0.001pt stroke.
There's more to it than that, of course, but from what I can see the only thing that prevents me from using Affinity Designer for manipulating the files I make for laser cutting/etching is that: I can't set my stroke width to 0.001pt.
Maybe someday vector programs will have a special "color" for "cut" or something like that. But until then, we rely on these cheats, and having a stroke width of 0.001pt is necessary to use vector graphics for laser cutting and etching.
Thanks!