Implementation may be strictly mechanical if you have everything planned out NASA-binder style, but surely there'll still be a need to adjust the plan from time to time? Then there's debugging and maintenance, both of which may not require all your creativity all the time, but if you're creatively sapped, you're walking into it with a few tires already slashed. At least that's what I've found in my own experience. It's not that you have to be creative constantly, it's that you have to be able to summon up the capacity to be creative at any given time.