By default in Gmail icon column of all items in your inbox will appear on right of the screen with which we can able to distinguish various items like messages with attachments,calendar invitations, Buzz posts , chats.Move Icon column labs feature for Gmail will bring this icon column to the left side of screen.
These icons visible prominently at left side of screen in Gmail.So enabling Move Icon Column labs feature will improve visibility of the icons .
To enable move Icon Column labs feature in Gmail , in Gmail click Settings >Labs scroll down to Move Icon Column Label entry and enable it.