[whpalmer4]

If you have a large store of attachments, or you need to be able to edit those attachments, you'll quickly discover that OmniFocus wasn't built with this purpose in mind.

What some people do is use something like Dropbox or DevonThink as the storage facility, both of which will give you links to the material that can be embedded in OmniFocus and referenced from either iOS or OS X. Neither is quite ideal: Dropbox doesn't get you offline access to the data, and DevonThink doesn't give you read/write access to the data. Of course, you have those issues even if you don't entangle OmniFocus.