The more detail we have in advance, the better the vehicle and driver match your needs on the day: whether the wheelchair is manual or powered, folds down or needs to travel in a fixed position, and roughly its size and weight all affect which vehicle in the fleet is right for the journey. The same goes for the passenger — whether extra time getting in and out is needed, whether a companion is travelling too, and whether the destination itself has step-free access, since that can shape where exactly the driver should stop.
Airport and station journeys benefit from a bit of extra planning specifically: terminal layouts and platform access vary considerably, so letting us know the airport or station and, where possible, the terminal, means the pickup or drop-off point can be agreed in advance rather than worked out on arrival. The same free waiting time that applies to any airport pickup covers the additional time this kind of journey can reasonably take at either end.
Because matching the right vehicle to specific equipment matters more here than for a standard transfer, booking with a little more notice than usual — rather than a same-day request — gives the best chance of the exact vehicle you need being available for the time you want.