Then you've used one without knowing, because somewhere between the ORM you used and the database was SQL, and that SQL was put together by the ORM's query builder

If by "raw dog SQL" you mean dynamically concatenating strings (conditionally, interpolating runtime values), that's literally a query builder, albeit a janky SQL-injectable one.

When you use query builder, you write a raw SQL code.

The benifit is you can insert user input right in string, and your query remain secure against injections. Additionally, a Nano Queries let you compose queries, and extend it, so you may build complex queries simply.

Let's say you develop a site to search something by its features, for example a movies. Your SQL query may easy takes 100-500 lines. Some part of this query will be a basic, some will be optional depends on provided filters.

With a query builder you may conditionally extend your query like that

if (userInput.rating > 0) {
  filter.and(sql`rating >= ${userInput.rating}`);
}

That's all Query Builder does. It let you avoid to write code like that

const values = [];
const getPlaceholder = (value) => {
  values.push(value);
  return `$${values.length}`;
};

const where = [];
if (year) {
  where.push(`release_year = ${getPlaceholder(year)}`);
}
if (rating) {
  where.push(`rating >= ${getPlaceholder(rating)}`);
}

db.query(
  `SELECT title FROM movies ${where.length ? 'WHERE ' + where.join(' AND ') : ''} LIMIT 100`,
  values,
);