For direct learning either way it works for me. I find I hardly need to preview or postview other than knowing that the books relate to the topic I am interested in for direct learning.
For photoreading with the intent to activate I wind up doing more of a postview now since I usually PR the book to get an idea of if it contains anything of interest to me so previewing is about 2 to 3 minutes at best. Just to decide what the book is about (e.g. fiction or non fiction, general idea of the topic). The way I see it previewing was already done when I first picked up the book 
. Yet even so I find reason to spend a bit of time looking for trigger words and previewing up to 8 minutes on other occasions. Usually for text that I want to activate in depth, I find the trigger words help me to pull out more from the book in the shortest time, it does improve comprehension.
That previewing causes you to slow down an analyse too much? Quite possible. I've noticed that a lot of doubts about ones ability to activate the book develop before actually photoreading. Thoughts like this is too complicated, or I'll never figure this out are harder to control. It is pretty clear that your mind is still functioning on a different 'wavelenght' after having photoread the text and placed it in your inner mind and is better able to hold onto the sense of curiosity.
I still see it as good practice to learn the photoreading process by doing a preview first. Many people when they pick up a book have not trained themselves to establish a purpose for reading. In particular where the text is mandatory for studies. They have no idea what they want or need from a book. The previewing habit trains the mind to focus on getting information from the text, laying a foundation that becomes faster with use, so that it seems that we are not even previewing a book anymore.
I think it pays to remain flexible. If someone asked me to 'read' a book that I have no personal interest or is totally new to me, I am inclinded to do a preview to prepare my mind for. Topics that I have an interest in, Photoread as soon as possible.
It's the same as acknowledging that sometimes activation will take longer than on other occasions, whether it is because I am not really interested in 'reading' or the authors style does not appeal to me. You need to remain flexible and find what works best for you and when.
Alex
