There are two kinds of liners you can get for a bead receiver. One is beaded only, and the other is a combo bead / overlap (i foget exactly what it is called). They have a bead, and then an extra 6" or so of materal after teh bead. If you have an overlap, then you use that extra 6" of material. If you have a bead, then you cut that extra off and just use the bead.
The other nice thing about the bead, aside from not having to take the top rails off, is it is "self leveling". If you have a liner with a border on it, with you have a bead receiver, it pretty much esures that the border will be the same height all around the pool. If you have an overlap, if you can even find a liner with a borded (they dont make many) it is a lot harder to get level all around the pool.
-dave