The point of knowing the Sunny F16 rule, is so you don't have to use a light meter.
Old
mechanical shutter film SLRs can shoot without batteries. Experienced photographers can just look at the light and say, "hmmm, I have ASA 100 film loaded, so I'll set the shutter speed to 1/125s, and the light is kinda shady so F8 will do." The light meter is inside the photographer's brain!
Later,
electronic shutter film SLRs came out, and those needed batteries to fire the shutter. Those had meters already. At this time it was still the manual focus era before Minolta invented current AF.
Now, your dSLR already has a meter. If there is no battery, there is no meter reading. But if there is no battery you cannot shoot!
So, since there's already a lightmeter, you might as well use it. It is fun to do it Sunny F16 style sometimes. Or Lomo camera style (typical Lomo cameras do not have a light meter, so the shutter speed is fixed at 1/100s and F8.0 - you're supposed to change film for different light conditions.)
Another technique to learn, to get good exposure, is the Zone Metering System popularized by Ansel Adams. The A100 had Spot Metering AEL Toggle, which really helps with learning this technique.
after reading ur explanation.. i remember sumthing about my fren nikon FG setting.. thanks dude.. understand n got some idea about how this thing works now