Snap the frame to the nearest keyframe in the scrub direction by holding down ALT.
When you're using autokey and quickly flipping through poses it's easier to use the mouse than the keyboard, but you don't want to be stuck somewhere in the middle creating unwanted keyframes. This simple plugin takes care of that problem.
Use it, abuse it, and if you improve it send me a code snippet so I can update it.
Easy installation: Change the extension to .py if it got converted to .txt during download. Open preferences in Blender 2.8, under addons, click Install and locate the file. Check the checkbox and save preferences so the tool is always there for you :)
Don't want to use ALT? Open up notepad, find these two lines
"elif not event.alt:"
and replace alt with ctrl or shift.
v1_0 - no keyboard shortcuts, only a button in the N panel
v1_1 - no more button, works by pressing ALT after dragging the scrubber
v1_5 - better handler management, fixed a bug that would cause lag and/or crashing. Fixed issues in script order execution