MacOS is a great system, built on great hardware. But with that hardware comes high-resolution Retina Displays which is a good thing.
However if you’re taking a lot of screenshots on MacOS, you’ll find the default file format is PNG.
PNG is excellent for retaining image quality, but has a high file size.
It’s easy to change the file format using the below commands in Terminal.
defaults write com.apple.screencapture type jpg;killall SystemUIServer
defaults write com.apple.screencapture type gif;killall SystemUIServer
defaults write com.apple.screencapture type tiff;killall SystemUIServer
defaults write com.apple.screencapture type PDF;killall SystemUIServer
defaults write com.apple.screencapture type png;killall SystemUIServer