base band is for frequency for the phone to communicate on. the reason for the new base band is probably because of 4G network. now you can choose old or new. but you wont get new roms with old bb.
now as far as i can tell on who would need to flash new bb this way are the one that didnt choose to get the official GB update. so everyone that has rooted there froyo and have been playin with roms, and dont want to upgrade and deal with rooting again will have to flash this way.
if you have GB 2.3.4 you should just have to root it get recovery and then youll beable to flash roms and the new kernel.
anyone do correct me if i am wrong , or confirm if i am not off my rocker