Why do you use `update collection`?

[IPNUISTlegal]

While skimming through your code, I don't understand why do you need update_collection variable here,
https://github.com/minhnhat93/tf-SNDCGAN/blob/master/train.py#L39

If i don't add update collection in the code.
just write like below

    with tf.control_dependencies([u.assign(u_hat)]):
        w_norm = tf.reshape(w_norm, w_shape)

d_real and d_loss both use the above procedure.
Is there anything wrong?
thx