hi!,
I saw in default HTML in Posts Disabled...Why is that? Is there any security reason or anything???

Yes basically a someone could run a script when posting a message that could gain access to your database or your php files...

I have no idea what they could do as I have no experience if ruining anyone sites but thats the general impression of what could happen..

   

Yep, security.

They can take your user and pass, insert iframes vith viruses, spyware, keyloggers..... if it is disabled.

DWho, it is less problably they take php files or touch the DB with HTML code as HTML is client side, but if PHP is injected.... they can even crush both client and server