The new Smart Labels are designed to complement the Priority Inbox feature that the Gmail team introduced last year. Like Priority Inbox, the goal with Smart Labels is to automatically help get mail where it needs to go.
Once activated, the feature creates new labels for bulk, notification and forum messages. Bulk mail includes mass mailing, promotional newsletters and daily offers. These messages are filtered out of the inbox by default (but still marked as unread if you want to check them out later). The "notifications" Smart Label works for things like account statements and receipts. The forums section is for e-mail from mailing lists or other large e-mail groups.
If, like me, you've already made extensive use of filters and labels to organize and categorize your Gmail inbox, you might wonder how Smart Labels are any different. The net result may be similar, but the fact that Smart Labels are automatic and customizable makes them pretty great.
For instance, my own inbox has filters and labels designed to move promotional mailings to their own folder. This is very similar to what the bulk Smart Label does -- except with Smart Labels, I don't have to manually add each e-mail address to a filter.
Smart Labels also work with existing labels and filters and can be edited like any other label. Existing filters can be adjusted to avoid being tagged by Smart Labels and users can decide whether a Smart Label group skips the inbox.
One of the areas where desktop e-mail clients -- notably Microsoft Outlook -- still supersede web clients is with custom folders and rules. With Smart Labels, Google is helping to close that gap.