Keep in mind that the number of decimals is a made up and theoretical thing after a certain point in any application. Let’s say you were working in miles (limiting your project to 22 units from the origin before you reach the limit of Revit’s geometry engine). You’ll obviously want to go smaller than that, but how small is practical?
Well for reference:
0.000000000000001 miles is 0.001 times the width of a Glucose Molecule. This is molecular scale, so unless your detailing looks like this you may have gone too far.
0.00000000001 miles is 0.003 times the length of a Cell’s Nucleus. If the building is going to have it’s accuracy verified using a microscope to confirm the location of each cell’s nucleons at the building scale, than you’d need this.
0.0000001 miles is 1.6 times the width of a Strand of Hair. Now hair has different sizes so this is a bit more out there as a unit of measure, but that is at least something you visually observe without a magnifying glass. That doesn’t mean the contractors can build to that tolerance, but you likely want to stop here as a means of accuracy review. If the building is off by a hair width and a half than I guess there could be problems with some edge case, but generally you need to account for this much movement of material via thermal expansion anyway - have them measure again on a cold or hot day if it is an issue.
At 0.000001 miles is 0.95 times the width of a Strand of Spaghetti. This is about 6/100ths of an inch or 1.6mm. You don’t want to go much bigger, though you may want to go a order of magnitude smaller.
Obviously if you are in different units (say meters, or light years) your ‘stop point’ will vary further. But at some point you will want to stop chasing precision as you very quickly hit the limit of our ability to accurately model the physical world.