When a vertical platform lift is placed in the corner of a room or within a shaft, it is not necessary to clad the rear of the mast in panels (as they will never be seen). Doing so, simply adds to the cost of the project. To this end, some manufacturers offer their lifts without these panels as a standard default. That way, they can offer you the most competitive price. You will often see these listed within the Optional Extras section of a quotation as Guide Backing Panels or Covering to Machine Side. If you are going to see the back of the mast then you will need to factor in these panels. If you are not sure whether or not these panels will be required – please ask the originator of the quotation.
With regards to Platform Stairlifts, it may be necessary to introduce Infill panels behind the rails, when the installation is stepped away from a wall or when it is possible to access the back of the lift through the guide rails (e.g. from your next door neighbours property or an adjacent staircase). These panels are applied in order to reduce the risk of injury to those in the vicinity of the Platform Stairlift.