A/B testing has been around for a while and is an extremely effective way of trying out changes to user journeys and/or logic flows within a software solution. The simple premise being that you can—through configuration, feature-flagging, or clever traffic-routing—send a predetermined number of users (or the transactions generated by use of the software itself) down different paths. This can help try out new features and/or functionality under controlled conditions normally within a production environment to prove or disprove certain hypotheses.
I won't go into too much depth regarding this subject—there are plenty of books and online resources focused on this subject that I encourage you to read.
Let's, for example, say that your business wants to see what the impact would be if they introduced a new design or subtle web page layout...