Use it for managing all files in active projects
I use EF in place of the Finder as well. All the files related to the project go into its library. From there, I can organize, reorganize, and (most important) use.
Why not just use the Finder? EF provides superior visibility and ability to manage the files. For example, the “title” can be quite different than the “file name,” so I can specify what’s in each file. Second, selecting a file automatically opens a window into it, and the in-window view can be edited directly (for most file types, not all). Highlighting and the like are instantly available. (In 10.5, Quick Preview has some of these abilities, but it’s much slower.) Third, it’s more flexible in how material gets organized.
The other big difference from using the Finder is EF’s ease of capturing files from diverse sources. With Finder, there are 2 methods: Save As, and Drag-and-Drop. But EF allows quick grabs from all kinds of sources and in all kinds of ways. Just the ability to automatically avoid duplicates is worth the price of admission - I don’t have to wonder whether I’ve seen the item before, I grab it “just in case.”
I could go on, but you get the idea. The main area I don’t use EF heavily is for files that I’m writing myself. There, the various facilities of programs such as Save and Automatic Backup seem inconsistent with EF. Maybe there is a way to merge them, but I have not taken the time to figure it out yet.