The Spain international had been considered a £50million flop until a recent upturn in form, which coincided with the appointment of his former Liverpool mentor.
Torres was Chelsea's first-choice striker for the first half of the campaign regardless of form, although Ba's arrival threatens that role.
The 27-year-old scored twice on his Blues debut against Southampton on Saturday and Benitez believes the former Newcastle striker will be good for Torres.
"Ba coming will be better for Torres, 100 per cent," Benitez said. "Not many players play every game in a top side, as he has had to, and now it will be positive for both of them.
"They will be fitter, maybe they will score more goals because they will have more chances and will be in better positions.
"Fernando is an experienced player and he knows football. We have spoken to both of them and they each know the role of the other, that they'll have a lot of games and will have a big part to play.
"Every session I can see Fernando is training well and trying to improve. Even when he's not scoring, he's working hard and doing things for the team.
"We have tried to fix things to improve his strength, a specific programme. If you do that, normally he can be quicker. It takes time, and I think it's improving.
"He's a bit quicker, but the biggest problem was he was playing too many games. Especially against QPR, some players were a bit tired, had too much fatigue. But having both Torres and Ba means both can do well."