There are a few things that I tweak when I get a new Macbook, one of which is the screenshot format (mainly because it doesnt natively render in Whatsapp). So I thought I would share the code snippet that you can run in Terminal to alter the default image type of your screenshots:
For JPEG use:
$ defaults write com.apple.screencapture type JPG
For GIF use:
$ defaults write com.apple.screencapture type GIF
For PDF use:
$ defaults write com.apple.screencapture type PDF
For PNG use:
$ defaults write com.apple.screencapture type PNG