When the wall behind the fixture will not carry the load. At a wall-hung pan there is often a duct panel or a prewall frame with no structural face available for a bar.

Rather than fixing into something inadequate and hoping, the load is shared with the floor slab, which is always structural.

It is also used where the required bar length puts one end beyond any available backing, so a wall-only fixing would be cantilevering much too far.

It occupies floor space and it does interrupt cleaning, which is the honest cost. A floor-mounted leg is one more thing for a mop to go round.

Against that, the leg is usually positioned in the zone beside the pan where nobody walks and nothing else is placed.

Where floor clearance is critical — a room designed for a wheelchair turning circle, for instance — the leg position has to be checked against that circle rather than assumed to be out of the way.

Into the structural slab, through whatever finish is on top of it, with the socket usually set to allow a small amount of height adjustment for floor level.

That fixing has to be done properly, since it now carries a share of the load that would otherwise be entirely on the wall.

Where there is underfloor heating or waterproofing in the floor build-up, the socket position must be coordinated before drilling — a point that is very easy to miss until the drill goes in.

It is better supported, which is not quite the same thing. The bar itself is typically the same section and material; what changes is that the load path no longer depends on one substrate.

That makes it more reliable in the situations it is designed for, rather than higher rated in absolute terms.

The rating still comes from the manufacturer's test figures, and those assume both the wall and the floor fixing are made correctly.

Yes, more readily than a wall-only bar in the same position, because the floor is available even when the wall is not.

That makes it a common retrofit answer when a room needs to be made accessible and the wall backing was never installed.

The constraint becomes the floor finish: drilling into finished tiling or a waterproof membrane needs care, and in a wet room the penetration has to be resealed properly.

It is one of the main reasons the product exists. A wall-hung pan hangs from a frame inside a duct, and the visible panel in front is usually not structural.

Some prewall systems offer integrated grab-bar support elements designed to be built in at first fix, and where those exist they are the neater solution.

Where they were not installed — which is most retrofits — the wall-to-floor bar is the practical way to get a supported rail beside the pan.

The rest of the washroom's bars, for the same reason as any other rail: a user's grip should not change between fixtures in one room.

Because a wall-to-floor bar is often added later, matching an existing installation is the usual constraint rather than choosing freely.

Where an exact match is unavailable, matching the diameter matters more than matching the finish, since diameter affects use and finish only appearance.