When I make hiring decisions, I’d like to see some art pieces in a TA’s folio - especially in junior folios since those people often do not know which direction they really want to go to. Knowing they have some good taste and some artistic ability puts me at ease when I assign them to projects where their skills will contribute to the look of a product.
TAs knowing about lighting principles, color theory, who have a good eye for realism, know about the daily troubles production artist face are so much more effective. All this can be used to your advantage to achieve a certain look, requiring less feedback from artists or art directors (e.g. when you’re going to work on VFX, lighting, rendering or shader related tasks)
Now I don’t require art to be perfect. It won’t be your job to, for example, model. But if you got your hands dirty at some point it shows me that you might have encountered some of the issues our artists deal with day in and day out and that, for example, what people are doing (in concrete steps) inside zbrush, isn’t a complete mystery to you.
For a TA folio, I don’t really think there’s a right way to do it, since TAs positions are often so different. Just think of all the fields tech art touches…engines, VFX, tools coding, rigging… if you really want to focus, you have to custom tailor a folio to certain position and then, depending on the position, decide if it makes sense to include art or not. But personally, I always love to see a little art skills in a folio.