Well, the hard drives are unlike flash-based memory drives can in theory have an infinite number of rewrites thus in theory it will not cause the hard drive to accelerate wear and tear. Nonetheless, they are mechanical devices and Eraser does stress the disk especially when erasing cluster tips. If you are erasing unused space only and erasing files instead of deleting them there should not be much seeking on the drives and it should not stress the drive beyond what it is designed for.
Note that this is my opinion as a software developer, not as a mechanical engineer so...
Joel