If you shoot tethered, the L plate can, depending on camera, often be a PITA when attaching the camera-side cord. BUT if you use just a bottom plate only, shooting portrait orientation can be less than ideal. You need to drop the ball over into one of it's notches and as one poster indicated, you need leg clearance for that.
Also, the BH55 isn't very smooth rotating 'up/down' when 'flopped' over 90 deg. I use the bittom plate only as I shoot tethered, but am considering moving to an L simply for that reason - another vote for the L plate.