It’s easy to add an app to the toolbar for quick access in Finder. Simply find it, hold down Command (⌘) and drag it up to the toolbar. Voila! You’ve got an app docked at the top of your Finder. To remove it, once again hold down ⌘ and drag it off the toolbar. This shortcut was available in previous versions of OS X, but in Mavericks, you’ve got to hold down ⌘.
Why pin apps to your Finder, you ask? Particularly when you’ve got a perfectly good dock on the side or bottom of your screen. There are a bunch of advantages. If you use different text editors to do things like code and write, just stick one or both of them up there and drag your relevant documents directly onto it. If you pin Mail or Messages, it becomes an quick shortcut to send a file. Or it can be handy if you do a lot of encoding and you pin a program like Handbrake up there.
But where this shortcut really shines is when you pin an Automator script — you can essentially include a button in your finder that does things like clear all files from the folder you’re in or automatically resize all images. The possibilities are endless for the power user.
[h/t Macworld Hints]