Food

I know about the moral that it may lead to an uprise and you would lose the province.

for the food not sure but other games does that and kill your troops it could be the case in here too

If you don't have enough food, the morale of your troops and of your provinces will drop. The troops will eventually get 'destroyed'.

Low morale matters because it leads to uprisings, which means you need to leave troops stationed there, and because it lowers production, meaning you get less of what that province produces every day.

Cool, thanks. So depleting enemys food production is considerable stratetigal aim.

Yes, but do not forget that food can be purchased on the stock market. So be sure not to devote too much energy and resources into lowering his food production as there are ways for him to overcome it. That being said, if he has to spend money to purchase food, he can't spend it purchasing rare materials/metal/oil that he might also need to produce units/perform research. So it can still have a positive effect strategically even if he can buy food.