1. Occupation Certificate (OC) is issued after the construction meets the building standards. A CC alone cannot legalise occupation; you must have the OC too.
Without a valid OC, your occupancy is illegal as it can be classified as an unauthorised structure by the authorities.
2. OC is crucial while applying for a home loan or loan to purchase a resale flat. You cannot even sell your property without a valid OC in hand.
3. Key amenities like water, sewage connection, electric supply, etc, can be disconnected in case you do not have an OC.
So decide accordingly.