Two other important considerations are Availability and Convenience. SPs are you listening?
In regards to availability, the last thing a hobbyist wants to do (or hear from an SP) is to give her more advance notice next time he's all boned up for you. You can't "plan" these things far in advance (like 1 week). A good erection is a bad thing to waste, especially if thoughts or dreams of you were its cause. Yeah, I'll just call you up to book an appointment for next Friday, duh!
In regards to convenience, the last thing a hobbyist wants to do (or have an SP do) is to haul ass half way across the city next time he's all boned up for you (assuming you are available). You can't "hold" onto an erection for too long unless you're on some magic 36 hr pill or a tantra master, especially if thoughts or dreams of you were its cause. Sooner or later the gasket is gonna blow. Yeah, I'll just call you up to book an appointment with the thought of having to drive through rush hour traffic, duh!
Moral of the story: be near and dear to a cock that is boned up for you when the moment is right and you're out of sight.