2. The swelling thing. I can't think of a single serious runner that believes their foot somehow elongates a full inch during the course of a training run, thereby causing them to suddenly hit the front of their shoe (the toeguard). However, you know what does often happen? A foot that feels quite snug in the store, can suddenly start feeling a bit tighter after an hour of pounding the pavement. That one spot that may or may not have felt tight in the store, actually begins to hurt. Now think about the shape of a shoe, and remember that the front of the shoe that tapers towards the toe is easily the most narrow. Keeping that foot from being crammed all the way into that area makes it less likely for the shoe to start hurting on the first long run and come back to the store as a return.
Huge+++, I've even returned a few models that I've picked up(Hoka comes to mind, I got a pair of their trail runners specifically as a part of my range gear and after like 2 hours using I've realised that they were way too narrow for me feet.