@awesomeopossum74 Those are good questions and may be going beyond my experience, but here are my best guesses at answers:
-Since the drawers sit on the runners, the drawers won’t help to hold the runners into the housings. That’s why glue and screws are used. I think the advantage of the housing is that, at layout, you can transfer knife nicks from side to side, knife in the housing location, cut it accurately, and know that the two sides will be dead on and will stay dead on forever. If you try to simply screw a runner on, perhaps guided by knife lines, theres a chance things will move vertically some time or another and disturb the drawer fit. To me, this is the primary reason for the housing: Accuracy. I suppose it also helps bear the vertical load, but I suspect screws are plenty strong for shear strength for just about any drawer, especially since you can put in a bunch of them. You can make things without the housing, definitely. See below and, also, Paul’s recent two-drawer organizer.
-I’m not concerned about a few inches of glue. The total amount of movement is proportional to the width of the wood. I think the elasticity of the glue will handle this. If you want to be extra sure, put a screw where you glued, too. Or, just use screws and skip the glue.
-You probably don’t need a slot for the screw, especially if the runner is housed. Just drill a little over sized (in the runner). You can calculate how much the side will change in width for a given change in moisture.
– I think you can make the screw as tight as you like and, if movement happens, the runner will slide under the screw. Wood movement is extremely strong. I believe rock was split at quarries by sinking dry wooden wedges and then wetting them. You can tighten that screw down firmly so that there’s no wobble and not think twice about it.
I’ve only made one piece that required considerations of these things. It was in a class. We were shown to make a frame as the drawer support, locate it accurately (no housing), and screw it to the two sides of the cabinet. It’s been a while since I last thought about this piece, but if I recall correctly, we made two of these frames, one that the drawers ran on, and the other to go above the drawers to keep them from tipping when opened (kickers). This piece (a chest) only had one pair of drawers, side by side, so the upper side of the kicker frame supported the bottom of the chest area. In other cases, it could have been the runner for the next layer of drawers. We may have cut a pair of temporary spacers, e.g., from thin ply, to hold the frame in the right location when screwing it into the sides to ensure no monkey business. I’d need to look in my notes.