Video giving another reason why orthonormal bases are useful. First reviews how to find the projection of a vector onto a subspace and then describes how an orthonormal basis can be used to find the projection. Simplifies the calculations to show they are the same as taking the projection onto the line spanned by each vector of the subspace. Also shows how to simplify the formula for finding the projection using the transformation matrix when an orthonormal basis is used. [16:14]