Usually, when you want your character to move from one pose to another, you need to set the starting key (say, at frame 50) and the end key (say, at frame 80). Normally, for a single swimming lane you would have to click "V" to set the first keyframe, then move to the end frame and move your character. Pretty simple. However for a complex facial movement that involves multiple facial features , for example, it is not that easy. Reasons are you don't always know which of the swimming lanes need to be used for each of the movement, as there are many of them. So I often end up making the move only to realize that another swimming lane needed a starting keyframe as well. Now you have to scroll all the way through the timeline window vertically, trying to find the swimming lane that contains that missing keyframe. Very tedious and frustrating.

One could say: use Face Puppet instead. Problem is: when you start recording with Face Puppet you will face the same issue. I often found that the face twitches in a weird way at the start of the recorded animation for some reason, making me rummage through the timeline again, trying to clean it up. Personally I prefer Face Key Editor 9 times out of 10. I find it easy to control.

Therefore suggestion. I really like how in the 2D Motion Key Editor there is a Set Key button (see screenshot)! It makes it so much easier! You move the cursor to frame A, press Set Key and then move the cursor to frame B and adjust the facial expression. No need to jump around the timeline chasing your tail. It would be great to have that button for the facial editor.