In Smallville one of the key tenets of the story is that the story is of Clark Kent before he was Superman, so during the entire show, he never flies and never wears his iconic costume. This is summed up in the famous rule the creators put in place, "no tights, no flights". The "no flights" rule is broken several times under various circumstances (mostly by people other than Clark), but the Superman suit itself only shows up deep in the final act of the series finale.
I have heard rumors that Tom Welling only agreed to play Clark Kent after hearing about the no-tights rule, and possibly that it was part of his contract. Having rewatched the finale scene, the camera cuts and angles appear to be very carefully chosen so that Welling never appears on screen wearing the suit; instead there is a series of wide shots where the actor is unregonizable (possibly even CGI?) intermixed with very close-up shots of Welling from the neck up. The closest we come is that he's wearing a Superman shirt under his work shirt in the very final scene.
Was Tom Welling ever the person wearing the suit -- the full body suit -- in any of the scenes that we see on-screen? If not, was that his choice or the show runners?