Hi thanulee,
Thanks for the files!
The points that you get after converting the Spline are points that might have been calculated continuously before. You can see the effect of those points when you place them in a Sweet or Lathe object. Set the Spline to Adaptive for example. While you change the shape of the Spline these Intermediate points will move, to get the best and most efficient distribution. Think of it as a rule, if the direction changes more than X degree, then place a new point.
At the moment you convert the Spline these will become editable points. The function is gone.
Why the handles are in the Bounding Box is not documented. For me, the handles are part of the setup and the point of the handle part of the shape defining elements. What you can do (do it on a copy, just in case) set the spline from Bezier to Linear, use the Axis Center to set the axis as you wish, and then go back to the Bezier. Do not use any other Spline options (e.g., Akima), as they will overwrite the Bezier settings.
All the best