For those not familiar with the term HDR it means High Dynamic Range. It is the difference between the lightest light and darkest dark in a picture. Each camera has dynamic range limitations. There are numerous programs available to bring the extremes back to an acceptable level. These programs are able to create some very extreme photos.
I tend to try to keep the finished photo to moderate levels. However, at times I edit over the edge a little. It can be applied to a wide range of subjects. Limitations are subject to personal taste.