The Elliptical trainer can be a useful training tool if you have some joint pain involving the hip, knee or ankle. If you have low back pain or calf problems, the elliptical can be contributing to your situation.
The benefit of the elliptical is that it does not load the extremity joints in a way that running on a treadmill or running outside will.
The cost of the elliptical is that it sends all the force into the sacral region. I often find that people that do a lot of elliptical have fixated sacrum's that don't nutate or counternutate as they should. Another issue that may arise is increased tension in the foot muscles. The heel always stays down, there is not the natural loading and unloading of the calf muscles and the fascia. This will potentially exacerbate plantar fascia and create an increased load on the front shin muscles, specifically the tibialis anterior.