The average nutritional breakdown of 8 ounces of tilapia is 40 grams of protein and 5 grams of fat. It has no significant carbs. So it definitely has a nutritional value, especially if you if you are on a diet which consists of a lot of protein and rather limited carbohydrates, like I am.
However it is very light because it's almost entirely protein, so it's good to stack it with something else as well. It's not enough of a meal for me on it's own. In this case I added avocado for fats, and some tomatoes to get more veggies in.
If you are looking for a fish that has more to it than simply protein, salmon has a lot of good fats in it as well, as long as you're counting what you're consuming. I eat both, depending on my day.