Creating custom spreads for a particular question is, in my opinion, one of the most potent tools one can bring to working with the tarot. Even before beginning a reading, if done well, just creating a custom spread can become as transformative and helpful as the reading itself. A well designed spread becomes like a mystical cosmogram, or even a talisman, onto which the symbols of the tarot project and interconnect with the matrix of meaning that has already been established within the nodes of the spread.
For me, a custom spread becomes more than a mental map of a situation, concern or problem - it becomes the anatomy of the solution. By taking time to devise it, I begin to seed the question into the mind of universe as well as my own mind; allowing it to create the kind of framework in which the language of the tarot can converse fluently and directly. It creates a space in which highly accurate responses can be evoked from the seventy eight mysteries depicted on the cards. Forgive my florid language! I just love the darned technique so much.
Taking time to create the spread around a concern also allows me to clearly think about the issue at hand; to crystalize it in my mind and solidify often vague or undefined fears, worries or related issues. Sometimes in the process you realize what the question is really about. Creating one with client, similarly, allows me to talk to the querent, attune to the problem that they are having and establish a meaningful dialogue before the reading even begins. They feel more relaxed, having been given the chance to explain and show me on paper where they are coming from.
It behaves a bit like diagnostic tool too in some ways; one which allows me to map out the client's headspace, motives and attitudes. As such its not a technique that is suitable for all my clients sitting for a reading - some don't know why they came, some are just curious tourists who come for a reading for fun or entertainment. Sometimes, time permitting, I like to create a spread with these sorts of people anyway: to help impress upon them that the reading is a bit more serious than that. Often they walk away very pleased and a bit more enriched than had I played the psychic mystery game with them, using a canned spread.