Define the context of offchain. It has different meanings depending on the context.
Offchain is generally considered when you deposit your bitcoin into some third party website/service and trust them to accurately keep track of the balance of your bitcoin. In exchange you will generally be able to instantly transfer money from person to person (instead of waiting 10 minutes for a confirmation), would not be at risk of any double spend attacks (assuming you trust the 3rd party service) and would allow you to avoid a TX fee.
The problem with this is that you need to trust some third party with your money.
Off chain transactions are clearly inferior
