While creating a new information for Drupal 8, I came across 2 approaches to create a new column on the entity table on database: * use hook_schema() (as I was used on Drupal 7) (https://gist.github.com/pedrorocha-net/3ed63f33b513d9c9ff86) * extends ContentEntityBase and use BaseFieldDefinition (https://gist.github.com/pedrorocha-net/70d6a84c3ddba1c5939d)
Both alternatives creates the table for me, with the data, but I think the latter already provides me more integration with other Drupal components e.g. Views module. By the other hand, being an "Entity" I believe brings some "weight" to the data, as it works with some wrappers(on Drupal 7 at least).
What i'm doing is port the Voting API module, so this question about extra weight can really impact on sites with more content.