The Manfrotto SYMPLA H-Offset connects two sets of SYMPLA 15mm rods in order to join a SYMPLA Shoulder Pad onto the second set. The top plane connects to a set already part of a SYMPLA rig, and the bottom plane allows a second set to be connected. (The Pad connects to the second set by way of an optional Universal Mount.)
The Horizontal Offset component allows two sets of SYMPLA Rods to be joined off-centre. The most common use is connecting a side-positioned SYMPLA Shoulder Pad on short Rods with a pair of long Rods holding a Variable Plate and Mattebox that need to be directly in front of the camera operator, so that the camera viewfinder or LCD screen can be more comfortably positioned and the weight of the camera and rig more ergonomically distributed.
You can also use the Offset to mount other compatible accessories via the added rods.