simplest case is that it can serve as a multiple staging environment, when you have loads of APP in a single code base (often startups going about prod-market fit). With docker tech shipping speed= production speed.
Without docker you are slowed down by 2x or more.Without docker, either you set up a lot of staging environments, which is not great and costly. Or you use one single testing environment and let each of you tech person wait for hours, wasting time, while QA tries to test one branch and you have another idiot deploying another brand on staging.
While there are more complex/useful cases, this is one simple biz value i get out of it for my team.