When should I use $wpdb->prepare, if at all?

Question

I have a hard time figuring out if I should be using $wpdb->prepare on my database queries in WordPress to prevent things such as SQL injection.

The $wpd

Answer 1

As I understand - the methods those have placeholders for query parameters ($wpdb->insert(), $wpdb->update(), $wpdb->delete()) don't need the $wpdb->prepare() method, and they are already safe.

But the others - those don't have placeholders, need additional sql escaping.