Assume you're using continuous integration processes which frequently update some target environments, so that every time there are some changes "you" can test your changes right away. That's part of the goals of CI, no?
But, also assume that you have other people involved in your test cycle, e.g. managers or customers. Makes sense to get other people involved in trying to review (break?) your upcoming changes, no?
But if you continuously keep delivering changes in the environment in which those other people are, seriously, trying to test them, then multiple issues may arise, such as:
theymight waste their time in reporting issues which, by the time they save the (in depth) report, they cannot even reproduce the issue themselves anymore (e.g because accidently you also ran into the same issue, and already fixed it in their environment).
youmight not be able to reproduce issues they reported, since the environments in which they ran into some issue, is no longer identical (you (!!!) might have overlayed their environment).
So what can you do (how to configure things?) to avoid such (frustrating) situations?