Maya has something called Buffer Curve Snapshot in its graph editor which allows to temporarily save a snapshot of a curve and then use it as reference when doing further changes to the curve. You can also use it to try to preserve the curve after simplifying it to fewer keyframes. Does Blender have similar feature and if so how does one access it?
Yes it is called Create Ghost Curves
It will create a snapshot in dotted lines of the selected curve(s). That lime can then be used as reference.
To clear the ghost curve it just click on the X icon again on the same place where you created the curve.
For older versions of blender select the curve, press the space bar to acces the search menu and type ghost curves. Then you can enable or disable the function.