Using the second tile gives the illusion of a glider moving against a background generated by the first tile. Using several of the second gives the illusion of a whole fleet of gliders.
Now, the other possibility is where the glider appears to move left just by a single cell every six generations. Once again we need a T5 tile, but with the T1 stuck on a little differently:
but the buffer column can be optionally inserted. Again that can be seen as a single glider, but repeating the process produces a fleet.
Their usage is that ether's or B's give way to a left margin, which can be followed by as many interiors as desired, terminated by one of the two right margins, followed once again by ether's or B-bar's.