There is always an ideal dimension for an image. Anything more or less than the ideal dimension results dysfunction. The ideal image sizes for social media posts are as follows –
In general, the ideal image size for Facebook is 1200*628 whereas for Twitter, it is 1024*512 and for Instagram, it is 1080*1080. Similarly, for LinkedIn, the ideal image size is 700*400 where Google+ requires 800*1200 and Pinterest needs 735*1102.
Learn more about Cropping:
Image Dimensions Definition by Webopedia
Image Dimensions in Common Usage by paulbourke