Mike is correct here - in other software products or products like Terramodel you would have used ARCBL command to create points around the curves based on an Arc to Chord tolerance specified by the user, and along long straight sections you would have to use Divide Line or similar to create the additional points along straight sections so that your surfaces would form more triangles to better represent the surfaces.
The time when you really need this is e.g. in Parking Lots where you may have an elevation on the outer curb at 2 corners, but then you have islands in the parking lot at say 1/3 and 2/3 of the length of the outer curb. If you dont sample the long straight lines, then all your triangles of the surface will connect to the 2 corner points which is unlikely to give you a great surface. Using the sampling distance adds points along the straight section so that there are true Z points near the islands, therefore allowing smaller triangles to be created and thereby creating a tighter surface in those areas.
If you have a rectangular Football field where the slope is left to right across the field and it is a flat sloping plane or even a crowned plane, you need less points along the straight sides than you would need in a parking lot.
The Project Setting is the default value used that affects all lines in the Project - however each line has a property called Override Segment Length and if set to Yes you can change it on specific lines to a different value - the video enclosed demonstrates the use of these settings
Hope this helps
Alan