Hanging a cabinet off a wall does not simply put its weight on that wall. The cantilever turns the load into a prying action: everything on the counter tries to rotate the unit away at the top and press it in at the bottom, so the upper line of fixings carries far more than the cabinet's weight suggests. The number to design to is an adult leaning both hands on the front edge, and eventually a child sitting on the end.
Blocking is a band, not a line. Solid stock let in flat between the studs, or 19mm plywood covering the full bay, running continuously across the width of the unit and landing on a stud at each end. It wants to be 200 to 300mm tall rather than a single row, because the mounting height moves once the basin and counter thickness are settled, and a band absorbs that where one block does not. No drywall anchor substitutes for it. On a concrete or steel-stud wall — common enough in island condo stock — the fixing method changes entirely and the capacity has to be established before the cabinet is drawn.
With no cabinet floor, there is nothing to conceal pipework behind. The waste comes through the face of the wall rather than up through the floor, and the trap has to sit inside the carcass, which sets a minimum cabinet depth and usually means a bottle trap or a slim low-profile fitting rather than a standard P-trap. Supply stops go inside the carcass clear of the drawer travel, or into a recessed valve box. Anything left hanging below the box is on permanent display.
The everyday payoff is floor. Tile runs through unbroken, which is what makes a small room read longer, and a mop reaches the wall — but only above a certain gap. Under roughly 200mm the void becomes a dust trap that is visible and unreachable at once. Losing the plinth also frees the height, so the counter can be set to whoever uses the room.