I mean, if you want to build up muscle by lugging around lower concentration liquid chlorine, then I guess it's doing harm since you're hauling less jugs? But otherwise no, it's the same stuff as normal bleach, just more concentrated. In fact it's recommended because you can be sure it doesn't have additives in it that bleach often does to make it scented/splashless/etc. Those additives aren't really good for pools.