Intuitive tab management
Spaces is a workspace manager for chrome. It treats each chrome window like a different workspace and lets you name and save each space. You can close a window full of tabs at any time then reopen it later and continue exactly where you left off.
Spaces keeps track of new tabs opened in each workspace and also tabs that you close. It also allows you to quickly move a tab that you are currently viewing into any other space - whether it's open or closed. Great for when you find yourself opening a tab out of context with what you are currently working on and want to come back to it later.
Spaces was developed to help users that tend to have way too many tabs open in a chrome window. It encourages you to move tabs that are not immediately relevant into a different, more appropriate space - thus removing it from your current window. This keeps your chrome session manageable - both visually and from a memory perspective.
Isn't this essentially just bookmarks with folders? Yeah, pretty much - but who uses bookmarks?