Some people just don't have to work to make living- life is more or less one great holiday to enjoy. Dilletantes often live on other people's money or on an inheritance. This kind of life makes it easier to indulge oneself into personal hobbies and interests. In the world of CoC many such dilletantes has a tendency to choose hobbies that in the end can turn out to be rather hazadous. Dulging into local history or helping out friends with dark secrets can lead to a situation where the dilletante wished he had a proper job. In the Hp Lovecrafts stories there is a number of such dilletants that end up in troubble. The perhaps best known one is Chrales Dexter Ward who pays dearly for his interest in family history.
If you choose to play a diletante you may have to decide why the character don't have to work for a living. This detail is often quite important for the character's background story