Many of us have the tendency to distribute images (JPG, BMP, TIFF etc) amongst our colleagues and friends as attachments. Instead sending the same as embedded images would drastically reduce the size of your mail, and hence would not hamper the performance of the mail server. So, images can be embedded instead of attaching in those cases where preserving the image format (JPG, BMP, TIFF etc) is not of utmost importance. The below is the original image size, and a memo's size after embedding and attaching the images.
Original Files icon.jpg 33KB icon.bmp 46KB icon.tif 49KB icon.gif 6KB format Embed Attach gif ~7KB 10KB jpg ~35KB 38KB tif ~7KB 54KB bmp ~7KB 55KB
From the above table, embedded images (TIF and BMP especially) drastically reduce the mail size compared to the attached ones.