It is entirely possible to stop after you've converted your photo to black and white. In most cases, however, additional enhancements will be necessary.
Corrective changes such as contrast and brightness adjustment, sharpening, and cloning are applied at this stage. It is much easier to make these changes after conversion than before. For example, it is easier to match gray tones rather than colors when cloning.
Aesthetic changes such as toning and adding simulated film grain are also done at this stage. Whether you do them before or after the corrective changes is up to you. Aesthetic enhancement is the difference between this:
and this: