This selects which stored software image the IP module boots from on its next startup: the one with the most recent timestamp, or explicitly image slot 1 or 2. Because a card typically holds both a known-good current image and a newly-loaded candidate image in its two slots, explicitly pinning this to image1(1) or image2(2), rather than latest(0), gives an admin deterministic control over which firmware actually runs after a reboot, independent of which image happens to have been loaded most recently. An admin who just uploaded a new firmware image into slot 2 for testing, but wants the option to revert without another upload, would leave this pointed at image1(1) until testing on slot 2 is explicitly confirmed successful, then switch it.