Oligodendrocytes are pretty cool. Picture them as blobby looking cells that find an axon, wrap around and around and around, then deflate - so what's left is lots of layers of cell membrane, and those in turn are each made of a lipid bilayer. Much of this happens well after a baby is born; oligodendrocytes are a major component of early brain growth. They more than make up for 'trimming' in which unused neurons self destruct and are cleared away by astrocytes. For anyone interested, I’d very much recommend William Harris’ Zero to Birth.

Myelin insulation increases the speed of action potential 200-300x as it turns a progressive (and very energy consuming) cascade into something that hops from gap to gap. Removing or reducing myelin insulation is an interesting puzzle. At a minimum, it would slow action potential, and now we have axons affecting the intracellular ionic balance of neighboring axons. Axons don't conduct electrons but waves of ionic potential, so there's not a clear parallel with removing insulation from wires conducting electricity. I would guess that one axon firing could slow or even suppress a neighbor through changing the intracellular ionic balance.

Just thinking it through.

Any neurobiologists care to correct me? I'm all ears.