IMHO, glue is absolutely necessary for long-term stability.
Only two weeks ago I made a small shelf out of some cargo pallet slats. I hand cut the wood and glued it together along the edges, staggering the ends, to make what looked like one ~8inch wide plank (the width of the slats varied a little) Think something like this:
11111111111222222222
3333333333333444444444
where each number represents another piece of wood. 1 was glued to 2 and 3, 3 was glued to 2 and 4, 4 was glued to 3, etc. I took some small pieces of scrap and screwed them to each board in my new wider plank to fasten them together while the glue dried. Getting overcomplicated I know, but I screwed 1 to 2, 2 to 4, and 1 to 3. This held them together snugly and it was easy to unscrew when done.
After the glue dried, I cut the new wider planks to the lengths I wanted and glued and nailed them into the shelf frame.
I haven’t quite finished yet. I need to sand down the front and back face to make them more even, and it takes some sanding to make cargo pallets look good anyway. But the wood held up fine with wood glue only to make the initial planks. I only ended up using nails for the frame because it was easy to do whilst the glue dried. Eventually I’ll need to seal the cracks and holes for the screws, but I plan on painting it. I wanted something that looked a tad buckly and uneven to match the trim in my bedroom, which is probably 70 years old.