The Spain international, who is widely regarded as failing to live up to his £50m price tag, was the Blues' first-choice striker until Ba's £7.5m switch from Newcastle last week.
While Torres remained on the bench for Saturday's 5-1 third round FA Cup win over Southampton, the newly-signed 27-year-old made an immediate impact, scoring twice on his debut.
"Ba coming will be better for Torres, 100 per cent," interim Chelsea manager 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."