A fixed fare means the price does not change with the route taken, but the route itself still matters for timing. Local roads, one-way systems, low-traffic neighbourhood schemes and school-run congestion all vary considerably between boroughs, and a driver who knows a specific area's quirks — which side street to use as a shortcut, where a particular road floods after heavy rain, which junctions back up at school pickup time — gets you there more comfortably even though the price is the same either way.
Outer London and the Home Counties bring a different set of considerations to inner London: longer average distances to the nearest airport, more reliance on A-roads and motorways rather than the London road network, and less predictable traffic since fewer alternative routes exist if the main road is blocked. None of this changes the fixed-fare principle, but it is part of why we ask for your exact address rather than just a postcode district — the precise start and end points genuinely affect the practical side of the journey, even when they do not affect the model used to price it.
If you travel regularly from the same address — a daily commute, a recurring school run, a regular business trip — a family or corporate account lets us build up exactly that local knowledge over repeated bookings, rather than starting fresh every time.