I use them sometimes with portrait sessions, and many times with my fine art images.
Using the right texture with the right image can take it to a whole new artistic level.
What was once an ordinary image, can be transformed into a piece of art, or a portrait with just the right amount of pizazz!
I have quite a few places where I get my textures from, so I though I'd link you to some of them.
Jessica Drossin Textures
Chasing Dreams Textures
Shadowhouse Textures (free)
Joel Olives Textures (some free packs)
Kim Klassen Cafe
Sarah Gardner Textures
That should be enough to get you started! If you have never used textures for editing, HERE are some videos on Jessica's blog to help you out or the Florabella blog.
Essentially using textures is just layering the texture jpeg image on top of your photo and using different blending modes and opacities to see how you like it. There are a million and one variations that can be done, in fact that's the problem many times, I can't decide which look I like best!
A lot of times I use the texture to warm up the image, so you won't necessarily see much in the way of actual texture, but just a tonal change.
So here's some of my examples-------
Now for a couple portrait sessions