Calender vs year in the depreciation profile

Hi ,

I have gone through the below link to know the difference of Calender vs year in the Depreciation year field of depreciation profile .…/aa573443(v=ax.10).aspx

But i am not clear about that which option i need to select either Calender or Year ?

Again we have same option in the Value model also . Why we need to have the same depreciation year field two forms like Depreciation profile and value models with the same options like Calender and year ?

Could any one help me ?