Surely some changes can be bad. Facebook Beacon was removed after some time for example. I'd like to know how to figure out what is the fastest to know if a c

Surely some changes can be bad. Facebook Beacon was removed after some time for example. I'd like to know how to figure out what is the fastest to know if a change is for the better or the worse. In the case of design change, I wouldn't expect a direct change in the metrics, it would impact on a longer term though.