We are building a project in ArgGis 10.2 were we create buildings using rectangles. Some of them need to be attached at one or more sides (they have common walls), so we would use snapping to snap vertex to edge to create a new building next to another. It seems to snap, but when zoomed in (1:0.3 scale) we can see that they are not snapped. at 1:1 looks good, but if we look even closer we see that the lines or point are not joined.
when working at such a large scale, you should check that you are not exceeding the precision of storage of your vertices. You would not see any difference when you snap a vertex (where the stored coordinates are already "rounded"), but an edge can have positions which falls between two possible coordinates. If you are going to use this in another software or at a higher precision, then I suggest that you insert a vertex at the position on the edge where you want to snap. Otherwise ArcGIS will behave as if they were exactly the same anyway.