When a client wants to take on more responsibility, give them the tools and training to do it. Don't hoard what you know. But protect yourself: handle special requests case by case, and renegotiate if the work load shifts significantly.
Never be guarded about your knowledge or your role. When a client wants to take on more responsibility and you don't see a great risk in that proposition, support it wholeheartedly. Even if it takes a few more hours on your part, give them the tools, training, and maybe additional consulting they need to be more independent. I'm not recommending that you burn the midnight oil on an ongoing basis or take big new blocks of work without a new agreement, but satisfying special requests for individual clients on a case-by-case basis can protect critical revenue.
