It depends on what you’re or the client is looking to gain. I have seen progressive muscle stimulation using body weight exercises. I often use a lot of body weight exercises, changing the modality as the client progresses. For instance: push ups: change hand placements, up/down, incline, decline, on a stability ball, walking, etc
Almost all body weight exercises can be changed in this manner changing which muscle fibers are continually recruited, increasing/decreasing the intensity of the exercise and keeping it interesting for the clients.