I noticed while watching the time-lapse that you sometimes changed your mind about which way to slide the vertices. Is there a general rule of thumb for which direction you should slide the verts? Or does it not matter as long as it doesn't effect the overall shape of the mesh?
Great question! I generally try to choose the side which is closest so that the resulting triangles are not so long and thin. There's nothing inherently wrong with long and thin tris, but they do sometimes mess with the UV unwrapping algorithm (not sure why) and often just look more messy visually. Beyond that, it doesn't matter as long as it doesn't effect the shape, as you already guessed.
Happy modeling!