I'll agree as long as you are then entirely ignoring the camera meter and not basing your exposure on any kind of reading from the built-in light meter. I'm quite comfortable doing that but I doubt too many photographers are, and as soon as you're going to rely on the camera meter then P mode gets the edge in efficiency over a large sampling of photos.
Joe
I don't entirely disregard the light meter, but I don't let it decide how I shoot either. What I often do is have it in spot meter mode, meter out the various zones in the frame point by point, see how many stops apart they are and then pick what I want my exposure to be based on that.
So, say for instance my subject is lit by reflected light, there is some direct lighting and some shadows, I'll point my meter at those three areas, and decide how I need the subject lit. Perhaps for some shots I would want the shadow detail and just let the directly lit portions blow out. In some scenarios I'd want to avoid blown highlights and let the shadows be underexposed. You're still using the meter then, but you're not letting the meter decide how you shoot either. You're simply using the meter to give you light readings.
And in P mode I'm doing precisely the same thing; I use the meter but I decide on the exposure and the shutter/aperture selection. I'm just doing a smidge less physical knob turning by using P mode.
Joe
Sure, but the issue becomes with a series of pictures. In P mode you'd have to adjust every single one. In manual you can get your basic setting, and then unless the lighting changes you just snap the next one. In P mode, if the camera's light meter reads some minor change in the lighting, it's going to attempt to 'fix it'. So, for instance say you're shooting a wedding reception indoors. The DJ lights might flash jsut a bit differently, and all of the sudden your camera decided to make a completely different exposure.
And I'm not sure you're doing less physical knob turning in P mode to begin with. Because you're fiddling with one knob to get the aperture/SS balance right, and the other knob to get the total exposure right. TO the extent it works like manual, it's just as much button turning as manual.
Going back to what I was saying, manual is better when you want your exposure settings to be consistent and not jump around with every little change in light in the field of view. P works when you're shooting quick one off shots, and you have no worry about consistency, you just want the camera to get you in the ballpark fast enough.
Again, all the non-scene modes have their strengths and weaknesses, the key is knowing when which each is the most efficient tool for the job.
My basic guide:
1) Manual: when you have time to set the shot up, when you're using manual flash, when you need consistency from exposure to exposure, when the shooting conditions are really going to give the camera's computer a hard time in picking the right exposure.
2) Aperture priority: When you need precise control of depth of field, but otherwise just need a relatively standard exposure. You can use exposure compensation a bit here and there, but if you're using it all the time, it's probably more efficient to just shoot in manual
3) Shutter priority: Your shutter has to be above a certain speed, depth of field isn't a concern, and you need as low of an ISO as possible.
4) programmed auto: you need a fairly standard exposure and shot to shot consistency isn't a concern. If you're changing the settings it gives you drastically, then you're effectively shooting in manual, but without the consistency of manual. Things can jump around without you really having any idea that they were going to, until it was 'too late'.
The problem I have with using P mode unless it's really by far the most efficient way is that it can surprise you too much. With manual, after you've taken one shot, you basically know what the following exposures are going to look like. With P, it can just decide to drastically change things out of nowhere. You take one shot and it looks great, you take the next shot and all of the sudden it's exposing it with drastically more DoF or another half stop of light. With manual, nothing changes unless I change it. That's both the good and bad of both modes. With manual, you have to change it, which is sometimes an inconvenience, but with P, the camera changes it, which is sometimes annoying. It remains my opinion that if you only use 1-2 of your modes, you're not using your camera to the full extent of its abilities, and you're making your life as a photographer harder than it needs to be.