Every save file contains your RNG seed. If a code promises "legendary cards," the RNG seed inside that code is static. When modern versions of the game recalculate card odds, an old seed can cause a checksum mismatch.
That string was his entire world condensed into code. If he ever lost his dice, he could simply paste that string into the Import box to resurrect his empire exactly as he left it. idle dice import save codes work
They are not a live cloud sync. They are manual snapshots. If you export a code, play for three more hours, and then import the old code, you will lose those three hours. Furthermore, codes may fail if they are corrupted, mistyped, or generated from a much older game version. Every save file contains your RNG seed