MacPaw's CleanMyDrive 2 is a nifty Mac utility that lets you clean up mounted drives, monitor their space usage and unmount them all in one click. It's a practical personal assistant that helps you manage all your connected drives.
It automatically cleans up system junk (DS_Store, Spotlight, hidden trashes, etc.) from external drives, freeing up disk space. The utility also shows the available space on the drives at a glance. The app works with network drives and knows how to deal with Time Machine volumes.
The "Eject all" feature allows you to eject all connected drives including DMG files with a single click. It doesn't sound like that big a deal, but is a convenient time saver, especially if you're working on a laptop and need to shut down and move out in a hurry.
The MacPaw solution is a no-brainer to use. Just click on its icon from the menu bar. From its preferences you can choose to have it launch when your Mac fires up -- or you can launch it manually. You can also set the utility to ignore volumes larger than 8GB.
There are drive space management apps that do more. But you want a reasonably priced (and free is as reasonable as it gets) tool for cleaning and unmounting drives, this little baby does its job with no muss and no fuss.
CleanMyDrive 2 requires OS X 10.10 or greater. It’s free at the Mac App Store but does tout in-app purchases.