The result is lots of time wasting junk emailing. Before you cc the standard list take a moment to be sure that everyone on the list should get the email. You may also want to consider an internal website for your firm that puts your email into mailboxes with different priorities. All fifteen messages have legal and malpractice significance, make sure each reply is appropriate and says want you mean. Replying to email can be so fast and easy that you may find yourself using a convenient form rather than the best reply.
Speed is important, but so is making sure the reply is correct for the situation.
At the present time, there appears to be only one rather innocuous kind of virus that affects Microsoft Word files with self-executing macros, which are sent via email. Microsoft has issued a patch to protect files from even this bug. Regardless you should still exercise reasonable caution. Make sure you have recent back-ups of all your files, if you use MS Word get the patch and update your firewall.