How brands fund it
The 5% base discount is funded by the seller (Seller Central) or vendor (Vendor Central). The 15% tier is co-funded by Amazon — Amazon adds the additional discount on top of the seller's contribution. Brands can also opt into tiered discounts to push customers from one-time purchases into subscriptions with promotional incentives.
Why it deserves more strategic weight
Subscribe & Save is treated by most brands as a tactical lever — turn it on, set the discount, move on. It's actually a retention layer. A subscriber locks in a brand at the consideration moment and removes that purchase from the next round of competitive bidding. The economics are closer to a DTC subscription than a retail discount: you're buying customer lifetime value at a known unit cost. The brands that integrate Subscribe & Save into their commercial planning — sizing the program against category penetration, optimizing pack sizes for monthly delivery economics, defending the funnel against trial offers from competitors — extract significantly more from it than the brands running it as a default checkbox.