Primarily, the function of synapses is allow communication between nerones in the nervous system.
Additionally, the structure of synapses means that they can perform further functions. Specific receptors for the neurotransmitter are found only on the post-synaptic membrane, and therefore this means that the impulse can only be transmitted through this membrane. As a result, this means that synapses ensure impulses travel in the correct direction through the nervous system.
As more neurotransitter diffuses across the synaptic cleft, the excitatory postsynaptic potential increases. It must reach the action potential of +40mV before an impulse is generated in the post-synaptic neurone. This means that weak impulses in the pre-synaptic neurone do not cause enough neurotransmitter to be released for an action potential in the post-syptic neurone to be generated. As a result, synapses are able to filter out low level stimuli that the body doesn't need to repond to, as such conserving energy. Furthermore, repeated low level stimuli can be amplified as each impulse arriving at the synapse causes the release of more neurotransmitter, resulting in one larger impulse in the post-synaptic neurone.Therefore, this allows the body to respond to the stimuli more effectively.