Hmmm, setting snap size to 0.001 might not work very well. Since that is the fitting tolerance, basically you don't want to create curvy details that are at that size - that's sort of more the lower limit.

Setting snap size to 0.001 might encourage you to draw details that are around that same size... So something like 0.01 for the lowest snap size would probably be better.

It's even better yet to create objects that are not so near to these limits at all... I almost didn't want to include kilometers or miles as units at all because they kind of encourage pushing things to larger or smaller numeric values like you're talking about.

- Michael

Of course!
But you can if you want insert precise measures (even in kilometers with the 3 décimal in the tool barre box or read it under the mouse movement! :)
Not obliged but a possibility :)
Sure at this scale 0.001 precision is an hard work on the Mouse wheel :D
And "snapping" is only good on the helpers and curve's points not on the grid itself!