What is the importance of shsh blob for updating to higher ios without upgrading baseband

I have jail broken 3gs with bb 6.15 old boot rom with ios 4.1. i tried to update it to ios 6.0.1 with redsnow to preserve the baseband but error of recovery mode occurs. i do not have shsh blob for ios 6.0.1 saved. after a day as battery died out i charged it and it restarts normally in ios 4.1 state. now in cydia it shows it is upgradable to 6.0.1 in the upper hand of home. kinldy suggest what should i do??