1. Right click to Cancel
In 3ds max, when moving, rotating or scaling an object (by dragging with the left mouse button), you can click the right mouse button to cancel the action and reset the object back to the position/rotation/scale it was at when you started dragging the object. I use this all the time in 3ds max and keep finding myself doing it in the UE4 editor only to realise it doesn’t work. Then I have to hit the undo button twice to reset the object.
2. Content Browser Lasso Select
Often when I want to select several assets in the Content Browser I hold down the left mouse button and start dragging to try and drag a rectangle lasso around them, only to realise it doesn’t work. I then have to hold down Ctrl and manually click on each one. I see someone else already asked about this a long time ago. An internal feature request was apparently created for it, but I guess nothing ever came of it.