The CDC link I have included may answer many of you questions. I Have highlighted some of the reasons for getting the vacine below.
http://www.cdc.gov/vaccines/vpd-vac/varicella/dis-faqs-ge...
It is not possible to predict who will have a mild case of chickenpox and who will have a serious or even deadly case of disease.
If your child gets mild case: usually miss 5 or 6 days of school or childcare due to their chickenpox and have symptoms such as high fever, severe itching, an uncomfortable rash, and dehydration or headache.
1 in 10 unvaccinated children who get chickenpox will have a complication serious enough to visit a health-care provider. Serious complications include bacterial infections which can involve the skin, tissues under the skin, bone, lungs (pneumonia), joints, and blood. Other serious complications include viral pneumonia, bleeding problems, and infection of the brain (encephalitis).
If a vaccinated child gets chickenpox the illness is typically mild, producing no symptoms at all other than a few red bumps.
Many of the deaths and complications from chickenpox occur in previously healthy children and adults. Before a vaccine was available approximately 10,600 persons were hospitalized and 100 to 150 died as a result of chickenpox in the U.S. every year. Since the vaccine, most of the healthy adults who died from chickenpox contracted the disease from their unvaccinated children.
Sorry for the lengthy psot,but it's good and accurate information taken right from the CDC. CDC also has info about exposure parties. I didn't read that info, but you should be able to do a search on their website.