This plugin does not apply for paths in groups. Please ungroup before. You can use Extensions → Arrange → Deep Ungroup) or Ungrouper And Element Migrator/Filter. This extension is similar to Convert To Polylines but has more control over the contours.
Draw some path
Run the extension
The higher the flatness value the less grade of detail the new polyline will have.
Get the result
Depending on the flatness we can get really smooth or really rough edges! Smooth paths have a lot more handles (points)!
Similar behaviour to flatten a curve can be forced by switching from to line type to curve type, but with less control for smoothness / segmentation.