What is the point in the Neuromuscular Junction?
After much searching on the internet I've found an answer to this question: the neuromuscular junction facilitates amplification of the motor neurone potential to generate a large enough current to depolarise a muscle fibre as muscle fibres have a much larger area of membrane (ie a larger capacitance) than neurons.
Source: Encyclopedia of Neuroscience: Volume One

The reason is the tremendous amplification of the neuromuscular junction. The amplification occurs since a small current is generated in a nerve can rekease large amounts of molecules of the transmitter acetyl-choline ($\require{mhchem} \ce{ACh}$), each of which can open channels in the much larger muscle membrane and can create much larger currents. In addition, a motor nerve fiber often branches profusely to innervate hundreds of muscle fibers, thus providing further amplification.
Finally, the capacitance of the muscular membrane has long been known to be much greater than the capacitance of the nerve membrane, because of the additional membranous systems, such as the transverse tubules in muscular fibers. Thus the capacity of the muscle to store charge is much greater than that of a nerve membrane and much more current must be supplied to depolarize muscle cells directly.