I tend to think it's not a good idea to just serve cats wet cat food. The belief behind this is that they need harder/crunchy dry food to help keep their teeth healthier. The may also get other nutrients from dry food, that they don't get from wet food. I think it's probably best to give your cat both wet and dry food.
However, studies have not shown any difference between a dry or wet food diet for dental health. Cats generally do not 'chew' their food and usually only crunch once or twice before it is swallowed. Cats also lack the enzymes that humans possess inside their mouths to help breakdown the food they eat.