Depends on the field - it happens that 1\1000 inch is a good tolerance for many machining operations, while metric doesn't have a convient round number close enough to that range to be useful. That doesn't slow down mathinists though, they know the fraction of mm tolerance they need to use and it is what is marked on their tools.
To give an opposite examples, in metric your speed limits are multiples of 10, in the us multiples of 5. Either works but metric has a better tolerance. deca-kilometers perhour would be even better - but no such prefix exists.
Metric-using machinists tend to default to 0.01mm (about 4 tenths) increments, with a default tolerance somewhere around 0.02mm. Default to one gradation on the indicator dial for US, 2 for metric.
More where the marks on the tool are. The marks are arbitrary, but round inch units happen to line up better with what you normally want than round metric.
Note that machining is the only place where we work with 1/1000 - that is a fraction that looks metric.