Rest is important after any training program because rest allows the body to become relaxed and help us to heel the muscles that teared up during training especially in case of strength training.
If anyone is targetting specific muscle group than at least 24 hours of rest is compulsory to hell the muscles that are torn during the intense specific muscle training. Therefore, in this case, up to four sessions of the same activity can be performed safely.
Some trainings which require repetition of heavyweight can require the rest of more than 24 hours.
