Typically they're used in a riser shaft or electric closet when you have a number of vertical conduits to run from floor to floor. Instead of core drilling (after concrete pour) or install numerous sleeves (before concrete pour) the masons will just form out a large slot. Then the EC comes in and installs a large steel plate with pre-punched holes sized for his conduits. The plate will cover the entire slot. We've done this when there was a need to run large numbers of riser conduits.