You should state which camera model you use and consider that other brands and models differ.
For Canon entry level series (xxxD, coming without dial for the thumb) one has to press a button and turn the dial to change the Ev settings in Av Mode, and exactly the same is requires to change Aperture in M Mode. No 'savings' here. Secondly, Canon deactivates the Ev function in M mode (somewhat redundant, actually). In M, the meter will always show real results, no offset due to Ev settings.
Contrary to your statements (which might be true for your camera) in Av Mode when changing Ev, the needle is not centered at 0 but offset according user input. It remains stationary to indicate the offset. Since the needle is shown in the viewfinder and in LCD display all the user needs to do is to check it. What more can the camera do than to highlight this?
I made a mistake about the EV indicator display. Thanks for the correction.
I'm using a D300s. Hence turning aperture or shutter speed is just working betw. 2 dials without having to press any button. Changing EV, however, needs to hold a button and turn the dial.
So let's just say shooting in Av (or A) mode, assuming a certain aperture is desired and is set, then follow by a shot taken. In order to increase exposure, I can either increase EV, or shift my focus point to a darker spot (which is inaccurate and affect AF). If I were to be in M mode, after taking the same shot as previous, all I need to do is to turn the shutter speed dial for the desire exposure compensation. Yes, the time saved is minimal but I dun have to worry about forgetting setting EV back to normal for the next shot at a different scene with different lightings and such.
I'm not a pro M only user, I still find useful situation for using Aperture priority such as situation when dynamic change of lighting happens so fast. I just want to make a point that using M mode is more of a practical reason than being egoistic, I used M mode right from the start when I first use my gf DSLR and I had grew very comfortable with it.
Letting the camera body to make decision sometimes gives me a little less confidence. Especially when you are taking some static scenes, where you are switching your focus point for the sake of AF but not metering for exposure, Av mode will automatically adjust the shutter speed according to your focus point. Yes, there are other mitigating function such as AE-lock and matrix metering instead of spot metering (I think this should help for metering for light) but I'm just so use to adjusting that one variable (shutter speed), I dun see how would using EV, or those listed functions can benefit me in such situation.
