In essence, offset correction is usefull for comparing rips by CRCs made from different drives and for avoiding generation-loss when making several generations of copies of copies. Also for CDs that follow the same reference as Andre has used, then those rips will be more accurate if a) overreading is enabled and supported or b) the "overreading part" consists of null samples, which will be padded by the app anyway if overreading isn't enabled.
Note: I don't know if fb2k has an overreading option at all, as i only use EAC/REACT for ripping/encoding personally.
In short: There's no reason not to use it, so check this site out for your specific drive :
http://www.accuraterip.com/driveoffsets.htmCU, Martin.