With the Battery icon, Option+click shows you the operating condition of your laptop battery, which gives you a sense of when you'll need to replace it. The four possible condition options are: Normal, Replace Soon, Replace Now, and Service Battery. It's a good way to either confirm or alleviate the suspicion that your MacBook battery may be near its end of life.
If you back up your Mac using Time Machine, holding Option will toggle a link to Browse Other Time Machine Disks in place of the normal Enter Time Machine function. From here, you can choose to recover backups from multiple drive sources. This feature can also be accessed from the Time Machine dock icon.