If you cut the T&G 1/4" thick by 1/2" deep, you will have some rather weak parts that are easily broken. You can go up to about 3/8" deep if making your own but you may have a lot of breakage if going much deeper. Not much difference between hard or softwood. A T&G joint, such as one might use for paneling, doesn't fit tightly all around and would require clamping the "ears" of the groove side tight to the tongue, clamping down, not together. That doesn't work well for most uses of a T&G joint, there can be exceptions.