Because the food is not cooked all the enzymes, vitamins and minerals are left. Especially by sprouting the grains and legumes you are increasing the nutritional content drastically and also making the grains more bioavailable.
And by not heating you are avoiding potential harmful effect of cooked food.
For example - heterocyclic amines (possible cancer causing by heating muscle tissues)
-advanced glycation end products (contributes to ageing and diabetes related
Lots of people decide to be on this diet for a short while for de-toxing.
It can be a great diet but also can be very unhealthy if not careful. (that of course is for any diet)
You have to make sure you chew the food very throughly to increase bioavailability of the food and also be careful with food-poisoning. More care is needed for children and pregnant, lactating women. Make sure you are getting sufficiant calories.
experimanting with Superfoods (such as maca powder, spirulina, bee-pollen etc.)can be a good addition to the diet as well