For enthusiasts who wish to "jailbreak" their devices—removing software restrictions to install unofficial apps and customizations—specific versions of iOS are often required. If a user accidentally updates to a version that cannot be jailbroken, they would typically be stuck. However, if they "saved" their SHSH blobs while Apple was still signing an older version, they can sometimes use those saved files to trick the device into accepting the downgrade, even after Apple has officially stopped signing that version. Evolution and Limitations
SHSH blobs (Signature HaSH blobs) are essentially "digital golden tickets" that Apple issues to verify your device and the iOS version you're installing. For the jailbreak community, they are the difference between being trapped on a buggy new update or staying on a custom-friendly version. shsh blobs
A solid technical feature about would focus on their role as the "digital fingerprint" required for the unauthorized installation of iOS firmware. Evolution and Limitations SHSH blobs (Signature HaSH blobs)
Even if you aren't planning to jailbreak today, saving blobs is a "better safe than sorry" practice. Even if you aren't planning to jailbreak today,
An SHSH blob is simply that signature saved to a file (or stored on a remote service like Cydia’s server) before Apple stops signing the corresponding iOS version. Once saved, it can be reused to fool the local restore process into accepting an unsigned firmware.