One thing I've found really really useful is handling multiple google users over multiple google sites.

I want youtube & google music to only use my personal account, so I never need to switch accounts, so google music and youtube open in their own container where only my personal account is logged in.

I want gmail and calendar to use my work account, so they open in the default container and automatically use my work google user.

I know that you can set your default google account by logging into it first, but I specifically don't want one default, I want different defaults for different google services, and that use case is handled beautifully by containers.