It helps the Republicans because he will not be counted as a Democrat in taking over the Senate and therefore the committee chairmanships.
I agree in that point but in actual voting in the House on all issues apart from WOT I see him voting with the Dems.
If Lieberman joins the Dem caucus ala Jeffords, I believe that he will be included in the Dem numbers for control of the Senate.
Unfortunately, it doesn't work that way; and he has already stated that if he wins as an Independant, he will caucus with the Democrats, i.e., vote with them in determining which party will lead the Senate.
Jim Jeffords did that when he switched parties in 2001, turning a 50-50 tie, broken by the VP in favor of the (R)s, to 49(R)-50(D) + 1(I). Jeffords got a committee chairmanship from agreeing to vote for Democratic control of the Senate. The dems controlled it until the elections of 2002.