The "attachment" is actually part of the message. It's something that modern (the past 15 years!) mail programs keep hidden from you. In Mail, do a View-->Message-->Raw Source and you can see the encoded attachments in a mail message.
If it's taking too much space and you don't want the attachment but still want the message then you can do a Message-->Remove Attachments, and the attachment parts of the message will be deleted.
Thanks for the info, much appreciated.
There are several reasons I can think of for wanting to have the a message at hand for reference, but not having two copies of the attached files. I do translation work and keep related documents categorized in folders by client name, some are work files that get edited and some are for reference only. Having the attachment saved in its original form is necessary, but having it buried deep in the mail folder is useless, and if it is a copy, that is a waste of HD space. Granted with the size of modern HDs, there is a lot of space available, I am only using 1/2 of my current 500GB HD, and most of that is taken by music or movie files, not work related at all, as those files are much smaller.
Thus, I found the other comments here a little strange huh...
, while your feedback was very well-informed and quite useful. Thanks again!