What are the reasons to constraint a column to be NOT NULL in SQLite?

As a newbie to databases and SQL, I wonder what are the pros (and perhaps cons) of placing the constraint NOT NULL when creating a table in SQLite.

I understand that it ensures that no NULLs can be inputed in that column, and that can be desirable. But besides that, I wonder if it improves performance of any kind -- e.g., by reducing the table's disk space or improving the speed of some queries.