The Smooth menu establish the parameters for the smoothing of the aircraft trajectory when changing from a phase to another, i.e to go from the final point of a phase to the start of the new one.
There are two different ways to smooth the path:
Line creates a linear track between the two points of the smoothed trajectory being possible only to set the position of the start and final points.
OGH creates a cubic curve where is possible to set the position and velocity that the aircraft will have at those points.
Smooth Configuration Menu
The other options that appear in this menu are parameters to limit when the smooth will be used or not.
The first one establish the minimum velocity at which the smooth will start working,
The second one is the minimum distance between the start and final points of the trajectory to begin with the smoothing.
The last option is the minimum time between points to use smooth, considering that the aircraft flies at the current speed.
All these options are safety features to avoid a malfunction of the system when the final and start points of the phases are close to each other.