Never fully bought into 'seasoned' , at least not in the sense that it adds any flavor to foods cooked on a grill. I do believe, it potentially helps protect against rust, if there is a kind of coating of oils and such on the inside of a grill. In pellet grills in particular, I think it can serve as a ash magnet , and keep some of the ash that might fly around inside a grill off the food.
My problem on my PG500, is that when I get up to my preferred pizza baking temperatures ( 650F or so ), all the seasoning burns off... I then have flaking burnt sort of seasoning that is all around the inside. I have to periodically use a wire brush or something to dislodge some of the flaking burnt 'seasoning'. Being the PG500 is stainless steel, rust isn't really a concern... but if you ever cook at these high temperatures, seasoning doesn't last long.