The most important is that very few, if any, people will actually open the file because of the risk of destructive VBA macros.  You may be sure that there is nothing destructive in your file, but no one else can be sure of that.   Few people will risk the possible enormous destruction that rogue VBA can cause. Code that may be innocuous or beneficial on your system -- e.g., resetting menus or options -- may be at least inconvenient on some one else's system.  You say there is no destructive code in your workbook, but we don't know you.

Attachments clog the network and servers, as well as the PCs of those of us who read and reply to questions in the newsgroups.  For easy retrieval, I store messages locally on my PC.  If you attach a 1MB file to a post, you've taken 1MB of real estate on my PC. It adds up.

Some readers, especially in areas of Europe and Asia, pay for both internet access and local telephone service on a per-minute basis. When a user has to download your attachment, they are spending real money, paying both their ISP and their local telephone company.  It may be free to you, but it isn't necessarily free to others.  The people who answer your questions are all volunteers -- none of us are compensated for our time and effort.  You're not likely to get much help from someone who had to pay to get your file.

File attachment takes time to download.  You may not realize it if you are on broadband connection (cable or DSL or corporate network), but downloading a large file takes a long time for those using 28.8 or 56.6 dial-up connections. 

Finally, attachments are almost always unnecessary. If you take the time to clearly explain your problem, provide in the body of your message some sample code and some sample data, some one will be able to answer your question.

You can certainly offer to email a file to individuals, but don't attach it with your question.

Of course, the newsgroups are open and unmoderated, so no one can prevent you from attaching a file, but doing so makes it less likely, not more likely, that you will receive an answer to your question. You don't want to antagonize those you who you are asking for help.  The generally accepted policy is no attachments.

For additional suggestions on using the newsgroups, see Hints And Tips For New Posters.