In terms of the overall structure of the film Pentangeli acts as basically a confused pawn in the whole struggle between Michael, and Hyman Roth. Gazzo effectively portrays this confusion, as well as simply showing Pentangeli as a man who acts as he needs to, and as the circumstance requires it. Gazzo though always also suggests the long history of Pentangeli in the crime world, a history that developed this particularly attitude he has gained.
There is not a great deal of Gazzo in the film,and I can't quite say he makes a huge impact on the film, but he most certainly does add to it. Gazzo simply becomes another fine aspect to the array of characters in the film, he is not the most interesting, or emotionally powerful character, but he does indeed find his place as he should in the film. It is a fairly interesting portrait of a man of very particular values, and a very particular history as well, not an amazing performance but a good one.