Your website pages will load faster if your file sizes are smaller. Search engines like Google favour websites that load faster, it is therefore important to keep your files sizes as low as possible.
You can sort files by 'File Size Largest' at anytime. This will identify any images that you may need to optimise.
MOBLE will automatically optimise your website jpgs when you upload them. pngs are also compressed, though if you are optimising for Google please use a jpg.