What does views_ensure_table() do? I see it often, $this->ensure_my_table() and I'm not sure what it does and why it is important when building Views handlers.
Taken from the API page:

views_handler::ensure_my_table


  Ensure the main table for this handler is in the query. This is used a
  lot.


It's just to make sure that the base table (node or user for example) that your handler needs is referenced in the query/actually exists.