The problem is what's cute in a 4 month old puppy is not so cute when they're an 18 month old adolescent who's jumping all over you, potentially wrecking your house and generally going mad from lack of training and stimulation
Training your dog enhances your relationship with them and provides an essential, constructive outlet for their mental and physical energy. This is especially essential as you have chosen a working Cocker, these dogs need training and ideally they need a job to do, be it working or some other activity to keep their minds and bodies active. A well trained and stimulated dog is still cute and funny and it'll be an awful lot happier, more content and enjoyable to live with too.
By the way - I'm not saying you can't let the dog on the sofa etc. if that's what you want to do, all of mine are allowed on the furniture but some level of training and something for the dog to do is important for their sake.