It's actually surprising this took so long: you can now attach files stored in Google Drive directly to an email within Gmail. That enables the attachment of much larger files (up to 10GB).
Gmail automatically checks the permissions on attached Drive files and prompts you to change them if the file is set for private access. That aside, the obvious advantage is speed: since the file doesn't actually have to get attached to the email, you don't have to wait for it to upload.
As with most Google features, this is rolling out gradually so you may not see it for a few days (it hasn't hit my account yet). It also relies on using Gmail's new floating compose window, so you'll need to enable that option to see it. (Microsoft's Outlook.com offers a similar integration with SkyDrive.)
Gmail and Drive - a new way to send files [Google Drive Blog]