Speed Pass Option
You can enable or disable the Speed Pass option in the Settings panel
The Speed Pass option might be involved when pasting an easing with the Paste Easing button only.
It controls whether to give priority to the easing curve shape or to the speed continuity. It works in a very specific, I’d say quite rare, situation.
I always leave it on, it works fine and I recommend you do the same. However, if you want to know what it does, pay attention to the following example.
Let’s say you want to copy the easing data from the first image keyframe and paste it into the second image keyframe:
As you can see, the first keyframe incoming and outgoing speeds are equal (in other words, the bezier handles have the same slope). This is essential to create a smooth animation.
When pasting the easing curve on to the second keyframe, what do you prefer? To keep the exact easing curve shapes (first image) despite breaking the speed continuity, or to maintain the speed continuity by adjusting the outgoing speed (second image)?
With the Speed Pass enabled (dot visible), you’re going for the second.
If the incoming and outgoing speeds in the first keyframe were different, that is if there were no speed continuity, you wouldn’t have to worry about the speed pass: speed would not be passed.