I think that in 99% of cases SOP's should be followed to the letter. If they can't be then they should be re-written.
SOPs at most carriers include a stipulation that not all situations can be covered, just as checklists cannot address every conceivable problem; and that crews are not constraint from using common sense. Deviations, in fact, are allowed for good cause, but they must be briefed by the captain.
For example: The SOP specifies that "max thrust" must be used whenever a tailwind is present. But what would be the point of that if, for example, you were empty, departing on a 13,000 feet pavement with a 5kts tail wind? Would you burn up the engines just because the SOP says so?
If during short final approach at 300 feet AGL in daylight VMC you had a GPWS warning, would you go around just because the SOP says so?
If the SOP says the recommended taxi speed is 15kts and you are backtracking on a 13,000 feet runway, would you deliberately slow airport operations because of your SOP's recommended maximum 15kts taxi speed? For the sake of operational expediency, would you not taxi faster than 15kts on that same runway where you had just touched down at 150kts?
How many pages upon pages of your SOP book would you have to "re-write" so that practical reality and good common sense could be followed "to the letter?"
