Hi!
the multicut tool creates a cut between two points you give it. It is a good tool to solve edgeflow issues where you need multiple cuts that connect to a point in the middle of a face, for example when you want to split an NGon or connect the edge of a Tri to the edge of another Tri. It doesn't restrict you in any way unless there is empty space within the cut. So you also can use it for cuts that need to look very straight and even but don't really align with the rest of the edgeflow.
The insert edgeloop tool splits polygons, it will cut all polygons within an edgeloop in the same ratio until it reaches an NGon or Tri, where it can't determine an opposite side and therefore doesn't know there to cut next. This is a lot faster that cutting polygons one by one. It's also really handy because the "multiple edgeloop" setting allows you to evenly distribute multiple cuts within a polygon or split a polygon precisely in half. But it has the restriction that it needs clearly defined edgeloops.
I hope this helps!
