Snip is a Mac utility that comes in handy whenever you wish to take a snapshot of an app developed by you to post it on your website. You can also use this program to capture error messages and share them with support staff. The application sits in your Menu Bar from where you can access the Preference panel, choose the Capture option, and quit the program.
This program supports only one output format: PNG. Some users might find this aspect pretty irritating. One solution would be to open the snapshot with Mac's default image viewer and export it to another file format. However, Snip offers you many useful features: it allows full-length windows capturing, lets you define a global hotkey for taking snapshots, identifies screens of other apps and enables you to easily capture them.
Another thing I like is the ability to edit the screenshots by using the integrated drawing and writing tools. You can add text content or geometrical shapes to your snapshots and resize them if necessary.
Furthermore, unlike other screen capture programs, this app has an option to auto-copy a captured image to clipboard. This feature comes in handy if you wish to alter the snapshot within other third-party tools.
Hence, I'd say it's worth installing this application on your computer. Plus, you don't have to pay a buck in order to use it on your Mac.