A site already printing labels holds a stock, and that stock has a format. In industrial and logistics settings it is most often 76 mm, inherited from production printers.
Then a Zebra ZD621R or ZD611R desktop RFID printer arrives, taking 25.4 mm as standard. Without adapters there are two options: buy the whole consumable stock again in the new format, or run two stocks in parallel, risking a shortage on one while the other sleeps in the store.
These adapters remove the choice. The printer takes both formats, the existing stock keeps earning its place, and bringing in an RFID machine does not trigger a procurement exercise.