99% of the time they are the result of a genuine effort made by flight ops departments to increase safety and efficiency
Genuine effort or personal opinions - therein lies the rub.
The problem is that a fair proportion of some SOP's are superfluous. To gabble a mantra such as "Auto-pilot engaged - Alt Hold engaged - Altimeters agree one two three all 1013 - I have VHF 1 my side - you have 121.5 your side - FD on heading both - Putting my seat back NOW -
I mean, for Christ sake we all have two eyes and it is obvious even to blind Freddy that continuous rote talking is not necessarily a good thing.
Now I made up that earlier lot but it is typical of some operators that unless you annunciate everything you do apart from scratching one's private parts (male or female) - then the operation is unsafe. And then there is the regulator who likes to sound important by insisting little things of his own personal preference is in print as an SOP.
The 737 FCTM at page 1.1 makes a reasonable point when it says "Conditions beyond the control of the flight crew may preclude following a maneuver exactly.
The maneuvers are not intended to replace good judgement and logic".
In another life I was PNF during a straight in NDB approach into a Pacific island runway length 5600 ft. The Boeing FCTM recommended gear down flap 15 and 150 knots until runway sighted then land flap as needed. It was heavy rain and low cloud and the DME worked fine for a change. The MDA was 700 ft but the vis meant we were never going to get flap down and stabilised by the time we spotted the runway IF we stuck to Flap 15 until visual. Sure enough the SOP pedantic in the LH seat had to go around when we broke visual too late to land - all because the book said stay at Flap 15 and 150 knots until visual.
We did another circling approach and despite the lessons of the earlier GA the chap still stuck rigidly to same flap setting and speed and the inevitable happened - we went around and this time we diverted 550 miles to our alternate which had no DME and an NDB 8 miles from the runway and it was raining when we got there on min fuel. All he had to do was dirty up at the original airport and we could have been stabilised nicely in time for becoming visual.
But this clown stuck rigidly to the company SOP and no deviation. He was no ace I tell you, as soon after he burnt out the brakes on a 737 with an unnecessary high speed abort on a 11,000 ft runway all because the SOP said max braking until aircraft comes to a stop. The aircraft stopped with 5000 ft to spare. The fusible plugs did their job and the red hot brakes welded on when he parked them...