For better or worse I have to use Lotus Notes on my client site.
As with all work environments, there are a lot of discussions that take place via email. Often times email attachments are involved.
What happens when 10 people continually send responses in an email thread, never removing previous attachments, while adding more? You get a 10MB file being emailed back and forth over forty times. It stinks. A lot.
It's not that hard to fix - "Reply without attachments". Now sure, sometimes an attachment previously sent is important, you may have to ask someone to refer to the attachment and feel you are making their life easier by including said attachment. I feel that is a rare occurence though, and people can quite easily just refer to the previously sent email.
If you are using Gmail, this is extremely easy. With Outlook, not that hard. With Lotus Notes it is actually fairly easy as they have their own version of threaded conversations.