Two is usually fine.
More decimaly only if the vertex need to snap to a prim, use the Unificator for that. The two decimals also fit most logos or curved patterns, even if you inline a circle, round it, not visible.
And if there are very fine structures, well, but LEGO does not print that accurate...
Remember:
1 LDU = 0,4 mm
0,1 LDU = 0,04 mm
0,01 LDU = 4 micrometers -> 6350 dpi!
More decimaly only if the vertex need to snap to a prim, use the Unificator for that. The two decimals also fit most logos or curved patterns, even if you inline a circle, round it, not visible.
And if there are very fine structures, well, but LEGO does not print that accurate...
Remember:
1 LDU = 0,4 mm
0,1 LDU = 0,04 mm
0,01 LDU = 4 micrometers -> 6350 dpi!