Clicker training has become more popular and many people use this when training dogs to sit along with other training activities.
The clicker provides very little input during the training process and, arguably, is another obstacle to the dog learning.
When the dog hears a click after a command, he anticipates a reward, normally edible. As you are giving your dog an edible reward when he sits ( in the form of his food or a treat ) there is not much value in adding a clicker.
Everytime you introduce something new into spaniel training you are introducing an extra ‘point’ at which the training could fail or become tricky.
You don’t need a clicker to train a Cocker spaniel to sit down.