There may be no harm, but if you do not correct the cause of the outbreak, you will get another one sooner or later. part of the challenge for me is to work at getting my tank parameters as balanced as possible and avoid any large outbreaks. This is not easy to do in a "box of water". Too many nutrients can cause cyano outbreaks, unfiltered water, too much bioload, all add to the problem. In the long run, if you want to enjoy a stable and lower maintenance system, these are the area's that you should be looking at.
JMHO