I know this is kind of apples vs oranges - but this Im primarily on a PC and I just noticed how much smoother this operation is on a Mac - 

Whenever I use segment or slip mode on a PC - the preview and program monitor switch to a 4 screen and this creates a lag and a stutter whenever I go into those modes and start dragging footage around

On a Mac these tools work much smoother with no sort of lag or stuttering when i drag - but the preview and program monitor dont switch to a 4 way box

Is there a setting I've got turned on that makes the PC behavior happen - or is this just the way it is. Both systems are on 2018.9

Well - I should have done more poking around - SHOW FOUR FRAME DISPLAY was checked on in my timelime settings. 

At least now I know what setting that does.