Oftentimes also means “often.” It is not wrong. You will still meet it in American speech and writing — a little old-fashioned, a little folksy, sometimes used when someone wants a slower rhythm than plain often. British English uses it less. It does not change the meaning; it only changes the dress. “I oftentimes wonder” and “I often wonder” say the same thing. Students do not need this word in their own writing; often is cleaner and fits more rooms. Though actually, the -s on the end is an old adverb ending, the same kind you see in besides, and in some dialects anyways: a little -s sitting on oftentime. There is a rarer form oftentime without that -s. Neither is more precise than often. They are just older coats for the same idea.