The ISO 100 setting is the most useful in bright light and landscape photography.
There are other cameras as well, where the base iso setting is ISO 200, for example the Nikon d40 is such a camera, but there are many others.
What are the advantages of the ISO 100 setting ?
The picture quality is here the best, the dynamic range is the widest and most useful and the colors are also here the nicest usually.
What are the disadvantages
Actually the disadvantage in some cases an advantage. But the disadvantage is that in low ISO setting we have the slowest shutter speed. In wildlife or bird photography it is very rarely to use such a low iso value. With long lenses of 400mm or even longer, we need a shutter speed of 1/1000s, which is only achievable with bright lenses which cost a fortune.
Long consumer grade lenses
With usual consumer grade lenses with a sharp apertures of f/8 – f/11 range very hard to get a 1/1000s shutter speed at ISO 100 setting.
Sunny 16 rule
If we check the sunny 16 rule, which means 1/100 sec at bright sunlight at f/16 ISO 100, means 1/400s at f/8 to put it simple. In Full sun perhaps sometimes possible but the target also need to be in the sun, which is not always the case.
When the slow shutter speed is an advantage
Sometimes for example at long exposure photography at night or daytime alike the low setting is beneficial. For night photography I mostly use the lowest possible iso setting, in order to keep quality, low noise, and highest possible Dynamic range.