In Mosman the windows are usually the reason the house is worth what it is. Large panes framing the harbour, often two or three storeys up on the downhill side, and almost always above a terrace, pool or planted garden where a ladder has nowhere safe to stand.

Mosman homes are designed around the view, which means large fixed panes and stacked glazing on the harbour elevation. That is exactly the glass that gets dirtiest and is hardest to reach.
The grime is a combination. Harbour salt settles as a fine haze and, because salt holds moisture, it grips the airborne dust and pollen that the surrounding canopy produces in quantity. Add sap and honeydew drip from overhanging figs and eucalypts and you get a film that is genuinely sticky rather than merely dusty, and one that returns quickly on the shaded side.
Access is the real constraint. Because the land falls steeply to the water, a house that is single storey from the street is frequently three storeys at the back, with the view glass at the top of that drop. Below it is usually a paved terrace, a pool or garden beds. There is often no safe footing for a ladder anywhere near the window that most needs cleaning.
Water-fed poles reach that glass from ground level. The purified water carries no dissolved minerals, so it lifts the salt and sap film and dries clear without spotting, and nothing rests against your gutters, sills or planting.
In Mosman the windows are not a detail of the house, they are frequently the reason it is worth what it is. That reframes what window cleaning is actually protecting.
A harbour outlook seen through a film of salt, dust and fig sap is a diminished version of the thing you paid for, and because the film builds gradually most owners acclimatise to it without noticing. The difference after a proper clean is usually startling for exactly that reason.
The practical benefit is access. The view glass on these houses is almost always on the downhill elevation, two or three storeys above a terrace, pool or garden bed, which is precisely where a ladder cannot be safely footed. That is not a job to attempt yourself, and it is the reason a lot of this glass simply never gets cleaned.
Reaching it from the ground with a pole also means nothing rests against heritage gutters, painted sills or planting, which on a period property matters.
Purified water handles the sap and salt film without detergent residue that would attract it straight back.
Water-fed poles, purified water and spot-free glass up to three storeys, without a ladder against your gutters.