We separate the camera exposure into two problems. Highlights we covered, the shadows we treat the camera histogram as our God. The bracketed exposures then being combined in Photoshop, giving us an image with beautiful shadow and highlight detail together. The very first priority, is recording the information with maximum quality. RULE. Breaking tones apart in Photoshop, degrades image quality, compressing tones does not degrade quality. Brightening shadows in software, breaks tones apart because we are making a limited tonal range cover more than they were designed to do, BUT, if we capture the full tonal range we do not need to brighten them in Photoshop, retaining quality.
As we expose the shadows brighter, we move them up the camera curve away from the flat compressed part, towards the straight part that gives more tonal separation. REALLY, REALLY IMPORTANT. As the tones gain more separation, this allows more room for additional tones to be recorded, the subtle tones. Tones that will never exist in the raw file unless you record them in the camera. The brighter you expose the shadows, the more tone you record. This gives you beautiful, rich shadow detail you will never achieve through software. Watch the histogram as you brighten the image. The bottom left corner is pinned to the graph, but the curve falls over becoming less angular and smoother.
The more we brighten the exposure for the shadows, the more the histogram curve falls over towards the right, but still pinned on the left at the black point. Imagine the shape of the curve, equated to taking off in an aircraft. Steep curve, brutal take off. Smooth curve, enjoyable take off. Same with tone; smooth curve means smooth tone and importantly, a mass of rich, subtle shadow tone. The question is, how bright do we make them? Watch the histogram, there will be a point where the histogram curve stretches towards the right, then can stretch no more; the curve pulls away at the black point on the left. Like pulling chewing gum off a wall, you achieve no more tone by making it any brighter.