Having just purchased an upcoming Samsung phone using their 0% interest I can tell you that the justification is to give you credit. I have the same with Best Buy which is 0% for a specific initial purchase. The bank (in the Samsung case is TD Bank) establishes a rotating credit line for you. The APR after is well established at the very high side of 29.99%. Nobody in their right mind should want to pay that much interest on any purchase. My last car purchase was below 3% APR.
Additionally the introductory rate will still calculate their 29.99% interest as if it existed since the first day of credit and will be applied to your balance should you ever be late on any single payment. At that time the interest is factored in as if it were always there and payments are adjusted accordingly.
You see, the bank wants you to pay their high interest rate. So they entice you with the 0% and hope you either finance more on that credit line (exempt from the promotional rate) or miss a payment and they can hit you with a whammy.
Specifically the question asks how this offer benefits Samsung. To answer that portion; it ensures a sale at full retail price of the phone. Samsung is just an agent between you and the bank. The bank takes on the risk for a potential high reward.