I believe Dave stated before that forum attachments are preferred. I've heard no complaints over bandwidth; this is a fairly busy forum, so he's not going to be paying for a bargain basement server regardless!
There might be legitimate reasons to avoid both attachments and free image hosts. Copyright retention is one. Many hosting sites claim ownership of material posted to them; every single status and photograph on Facebook, for example.
I believe this forum makes no special claims to submitted material, so that's not a big deal, but if you want to minimize file duplication, or retain the ability to modify at will, you might choose to host files yourself.
Personally, I almost always host images myself, but that's because I have it set up for basically one-click uploads.
![Tongue :P](https://www.eevblog.com/forum/Smileys/default/tongue.gif)
Tim