Gil Fronsdal leads a Guided Meditation Dharmette Practicing with Imagination. Yes can be called an attitude to being present and being open, being there.
If you're doing walking meditation and paying attention to your feet as you walk and foots coming down to the step, rather than saying stepping, you say yes as you make the step. Or breathing, some people use mental notes as they breath and would count their breath and might say in and out rising and falling instead say yes to breathing.
The practice of saying Yes is associated with human capacity for imagination. This little bit using some imagination or some conception of what Yes feels like or history of it or affirmation or acknowledgement or yes or some opening to it. And human beings are using imagination all the time. Sometimes imaginations can be very subtle if not necessarily seen that we're doing it. But it can create kind of vernier or veiled through which we see their experience. We can have the imagination that there's danger and some people are constantly living in a world that they think they're in danger,