Yes OCR can be used to reduce the file size of a PDF as pdf is image based and OCR converts that image into text which reduces the size of the file. This may make great change to the file size and it can reduce the overall burden of data.
So if PDF is image based how does OCR reduce the image? OCR relies on the fact that a file is just numbers, numbers are a linear pattern, it follows the rules, and it is possible to find the patterns within a series of numbers. PDF files are based on text so OCR is a more natural extension to make PDF less of a burden. For every image that is found, there must be an offset number, in this case OCR will find a number that will be zero. This will then be converted to text and displayed. This reduces the file size of a PDF considerably and also increases the amount of data that can be stored within a PDF. Using OCR within the PDF Writer allows a huge amount of editing to be carried out when PDFs are being created. So this is a significant increase in productivity and is the best.