I have two models on my app: `person` and `person_bio`

`person_bio` has 4 fields:

a person association(foreign key), a text column, a `source_id`(foreign\_key) and a `bio_url`

A co-worker advised me to put all the new fields on `person` instead, since it will be less complex, and less heavy to insert/update

What would be the best choice, given that `person` has millions of records? 

A bio would be optional, which means, we would have many NULL values, if the columns are inserted on `person` does that impact performance on mysql?