Significance of DPIS during add to asset in mass addition for calculated depreciation method over as

During mass addition if I choose add to asset option and check the amortize option then in that screen there is no place to mention the period from which I want to ammortize.

So how does system knows from which period to ammortize.

Also what is significance of DPIS during add to asset because even during add to asset system allows to put any date on or before the current period as DPIS.

Does the system use this DPIS of add to asset(cost adjustment) to derive the period from which it need to charge depreciation.