That means I can have an even more focused inbox that just contains things I need to think about / respond to right now.
In comparison, I still use regular gmail for my work email and I have maybe a dozen emails sitting in there that I don't need to do anything about right now but need to follow up on soon.
IMHO, Inbox basically takes the stuff that inbox-zero folks had to learn to do manually, and makes a lot of it automated. It's particularly great on mobile.