SHSH's allow you to downgrade firmwares in the event you don't like the one you're on now. It's not required you do it but highly recommended. You can save your SHSH's on your phone by downloading iSHSHit from Cydia. You can then email the SHSH's to yourself for safe keeping. Or use the Tiny Umbrella method in the event you find a computer to use. TU only takes about 5 minutes or so to save your SHSH's.