If you were to set your resizing limits to 1000×1000 and you uploaded an image that was 900×900 in size, normally the plugin would do nothing.
If you force the jpeg re-compression then even if the image isn’t resized, it will still re-save the image at the compression level you assign (e.g. 90).
You may want to do this if a lot of your users are uploading photographs which are not breaking the resizing limits, but are being saved with ’99’ jpeg quality. E.g. if they select “highest quality” setting in Photoshop.
Usually images can be saved at ’90’ quality with very little loss of image quality, or ’80’ with very minor loss of quality.
Typically, a 1024×768 JPEG at 99-quality would be about 400KB in size. Re-saved as 90-quality would reduce it to 200KB, re-saved as 80-quality would reduce it to 100KB, etc.
Hope that helps!
Phil
