Drawing from reference photos is fine, I do it all the time. I also draw from life now and then to keep my drawing skills sharp. Drawing from life makes you interpret three dimensional form into two dimensions, and that is a huge part of what realistic drawing is about.
Often when you draw from life you have to make a decision to draw a value lighter or darker than it really is. For example, in many lighting situations a reddish brown horse would almost disappear in a field of green grass if all color was removed. In grayscale, the horse would be the same value as the grass. As an artist, you would need to make a decision about how to interpret what you see.
After you have had lots of practice at drawing from life, decisions like this come more easily. And a good life drawing foundation will make you a better artist in other ways too. You learn composition, texturing, space, form, and linear beauty.
