Thinking of Guru all the time of day and night will give us a great power to protect ourselves from Samsara

The idea to practice Guru Yoga is to receive the blessing from Guru, which means one becomes inseparable from Guru. One doesn’t have to have too many thoughts but only faith, only mindfulness, only visualization of Guru. That’s the result of the practice Guru Yoga. And the high masters like Milarepa really achieved that kind of result and reached that kind of level. In his mind, there’s no physical, regular guru separated from him, therefore he was able to receive all the blessings, all the power from Guru.
I think people have read about Guru Yoga in “The Words of my Perfect Teacher” and other books. They describe in similar ways how to visualize and think of the Guru during day and night. And when we do that, it’s always important not to forget about Guru, His kindness and the practice because when we forget, then we create negative karmas. If we remember this, then probably we are able to protect oneself from creating karmas. Therefore, this has such power to protect oneself from being in Samsara and give a lot of benefit.
Visualize that the root Lama is Guru Rinpoche. When we visualize our own Guru, we visualize He is a Buddha. We don’t visualize the Guru in the regular ordinary form, like a human being, but we visualize the Guru like a deity, or Buddha or Dakini. Because when we see the Guru as an ordinary person, then this may cause some impure view. Therefore, we need to develop our pure view all the time toward everything, especially towards the Guru.

Hungkar Dorje Rinpoche, “GURU YOGA: Bless Me So That Delusion on The Path Will Cease”