File powder (ground sassafras)

I never put the file into the pot of gumbo. Can't forget why my mother said not to but, she did so I don't. But we sprinkled it atop the gumbo and rice in our individual bowls, like pepper.
I've never used file in anything else.

You can skip the file if you use okra. They both provide thickening properties. Okra is cooked into the gumbo, file is added to the bowl at serving time. Most recipes call for one or the other. I've never seen a recipe call for both, nor have I ever used file for anything else.

Call me redundant but, while I always use okra in gumbo (don't know how to make it any other way???) we add a sprinkle of file powder as well. It adds just a little more kick.

yep, sounds like you're using the file as a flavoring rather than a thickening agent. It's all a matter of preference. Some use rues for thickening, some use okra, some use both, each with or without a table sprinkle of file for flavor, some use neither rue nor okra and use file to thicken the broth -- added just before removing the gumbo from the stove.

I think most folk's preference is based on tradition and "sliminess" tolerated. Gumbo can be slimy if the file cooks too long, or it can be slimy if the okra isn't cooked long enough. I'm not a big okra fan (I once told my mother that I liked her chicken gumbo except the gumbo part, meaning the okra) so I use file. I've also been known to use a rue which is sacrilege in some kitchens.

I always start with a roux and add the okra. And then a sprinkling of file before the first spoonful. I had gumbo at a casino in Baton Rouge last weekend and was surprisingly disappointed by it's lack of flavor. Bummer.