Hello docfi,
Thanks for visiting the Apple Support Communities and asking about your MacBook Air. I believe you are only sleeping the computer, instead of fully powering it off.
1. When you close the lid, the computer will go to sleep. This article talks about some different options: Use the Energy Saver settings on your Mac - Apple Support
"Put your Mac to sleep
You can save energy by putting your Mac to sleep when you're not using it. When your Mac is sleeping, it's on but consumes less power. And waking your Mac from sleep is quicker than starting it up after it's been shut down.
To put your Mac to sleep immediately, do one of the following:
- Choose Apple () menu > Sleep.
- If you use a Mac notebook computer, close its built-in display.
- Press Command (⌘)–Media Eject (⏏).*
- Tap the power button on your computer.*
*These options don't apply to MacBook Pro models with Touch ID."
2. To fully power your Mac off, there are a few options depending on the model, but the most common way is to click the Apple top left of the Menu Bar, and then click shutdown. How to turn your Mac on or off - Apple Support
3. If interested, there may be other options or features available which can be used for different things: How Power Nap works on your Mac - Apple Support
Thanks and have a wonderful day.