This idiomatic phrase means without other factors in consideration, but it is just as often injected for emphatic purpose. Although old fashioned to some ears, the phrase is fairly modern, with popularity rising sharply since the late 1800s. Avoid the phrase in careful writing, since cleaner wording can replace it in likely all cases. Prefer The weather was not solely responsible for the poor attendance, which is clearer in intention and cleaner in prose, to The weather, in and of itself, was not responsible for the poor attendance; likewise, prefer Knowledge alone (or Knowledge itself) is worth pursuing to Knowledge, in and of itself, is worth pursuing.