A majority in name only still means that they can control the agenda of the Senate, and subpoena powers of the committess.
People who say it doesn't matter who controls the Senate really have little understanding on how Washingtoon works.
What happens if Chaffee pulls a Jeffords? Do you really think that if it were left to him, he'd want the Republican leadership to run the show? I do think it matters who controls the Senate. However, I believe that if Chaffee is the 50th Republican, it won't be long before there are only 49.