The most important difference between the two is the speed at which the impulse travels. As the distance between synaptic junctions is shorter for electrical impulses, they travel faster. Chemical synapses use neurotransmitters to send messages which are slower. In an electrical synapse, an ion current flows over a gap junction between neurons. It is bidirectional, and there is no delay. The advantage of electrical synapses is speed and precision such as in the heart where the muscles must be synchronous.
The advantage of a chemical synapse is that one neurotransmitter impulse can cause the action of multiple muscle cells, for example, whereas an electrical impulse is less versatile, mostly being used for sudden reactions, such as reflex actions. Another advantage of the chemical synapse is that it can be affected by multiple neurotransmitters, and then make the decision whether to pass on the information (make an action potential).