Yes, we have to be careful when we are actually absorbed in any type of reflection, to make it safe. I often give the example of someone hammering a nail into the floor while their doing Compassion/Lovingkindness to all living beings. It's probably not appropriate at that time because they may hit their thumb and hurt themselves. We have to see when it is appropriate to do reflections and when it is appropriate to be just here observing our actions. This is why we encourage people to do reflection more in a stationary posture rather than in a moving posture.
I'll give a true example of someone who got very spaced out, and was in a trance-like state. They were doing concentration practices, and they got so spaced out that they walked off the platform at the Bangkok train station and broke their legs. So it's quite important to have mindfulness when we are walking, otherwise we may get too spaced out. When we are reflecting we can get so absorbed in our thoughts that we are not aware, and we may be walking into the street and a truck may be coming. We have to see what's appropriate.
This is sometimes the danger of just repeating the phrases, because the concentration can increase to a very high level and we can space out and go into a trance-like state, which can be dangerous. Reflection does not have as much danger, in that we are thinking but we are not getting our concentration up so high that we get into these concentration states. But still we have to be careful about thinking and walking and doing, especially when we are chopping vegetables.
However I have been in particular situations where I've seen some difficulties arising in the mind, and then some phrases of a memorized Sutta may come to me at that particular time and it's appropriate. It's very helpful to have a practice in these types of things. This is why we encourage a short form of the Five Reflections, so that it becomes a very deep groove in the mind. We also encourage going into it in more depth, but if we have this short form of the Five Reflections then we may get into situations and the mind will bring up the appropriate short reflection, with all the understanding of all the deeper reflections we've done. It's very powerful for changing the wrong view in the mind. This is what is really helpful, changing the wrong view.