@Anonymous
If you want every polygon to overlap each other and occupy the full UV tile space there are a few things that will make this easier.
Copy and Paste. Once all your polygons are detached, you can actually use copy and paste to have them overlap each other. It's a little quirky in how it works, since you need to select the poly you want to paste on top of and right click then "copy". Then you select the polygon(s) you want to paste and then right click and select "paste" . the polygons should line up on top of each other. What's cool is you can paste multiple polygons at once.
Snaps Toggle. In vertex mode with Select by Element on you can drag and snap 1 vertex of a poly to the corresponding vertex on another poly. If the polys unwrapped are exactly the same size, then all the verts will line up. For polys that are not the same size, you can line up the parts you want with this technique.
Sometimes you may have polygons that are coplanar, so to detach these polygons flatten mapping will not work even if you set the polygon angle threshold to 0. To detach coplanar polygons select them and then convert the selection to a vertex selection (Ctrl + Left Click on vertex mode). With the verts of these coplanar polygons selected, click on "Break". These polys will now all be detached in the UV editor.
Some useful tips I picked up on this forum. Hope they are helpful.
