Django Forms primarily perform two functions within a Django application. They can render html fields and related tags like labels and legends and they can also validate and process data submitted to a view.
In terms of a codebase they typically live in their own file,
Forms are the most common entry point to business logic which is normally going to be saving some processed data to the database. This keeps what is happening from a view to a form to one or more models clear and explicit, which leads to easier readability and maintainablity. Essentially your future self or teammates will thank you.