Where do you decide to 'cut' the image set or scene when it comes to posting them on free sites?

Do you show as much as possible when it comes to the actual 'action' in an image set/scene or do you try to cut the set when it comes to showing the good stuff to entice the surfer in to joining whichever site you are promoting?

Do you think there is a 'standard' when it comes to what we should be showing on our free sites based on the amount of images in a content set or the length of a movie scene?

Your thoughts, where is the ideal place to cut off from an image or movie scene when it comes to building free sites?

Regards,

Lee