thank you for this post and taking the time, but say for example ive keyframed XY and Z in position and then ive also applied some custom bendy tangents from the first keyframe and on the last. Adjusting the f curve in this case i always find drastically change the tangents and the way the object goes from point A to B, when in fact all i wanted to do is adjust speed and easing on this cutom path i have created.
Usually in these situations i just opt to use spline path.
Thanks