A curve it is always a polygon. In different cases we need different accuracy. Setting from the start the best is not a good idea because in such case a polygon will contain to many segments. This will dramatically slow down calculations.
As a solution i propose custom curve approximation scale option. User will have a global settings to set value by default. and also option to set custom value for each curve.
In such way creating draft can be made with low accuracy and only later for finished result will be used better accuracy.