Eventually all APEX developers need to have multiple versions of the development environment open at the same time. A simple example of this is if you’re working with two pages (Page 1 and Page 2) that are dependant on one another. You constantly have to toggle between them as you can’t have two tabs open for development (one for P1 and one for P2).
Multi-Account Containers segregate your cookies by containers. Aside from APEX development you can also have multiple instances of Gmail or Office 365 opened in different container tabs.