Freshness
Every route is computed against the newest complete forecast from each model, not against a cached daily snapshot. Models update on their own schedules: global models several times a day, and the US fine-scale model hourly.
Common areas are prepared ahead of time, so for most requests the latest forecast is already on hand and routing starts quickly.
The top of the screen shows the forecast range the route covers and the wind reference height, which is what polars are quoted against.
Data size
A global forecast covers the whole planet at many points for every variable and every time step. Downloading enough of that to route an offshore passage would run to hundreds of megabytes.
You download only the corridor of water your route could cross, compressed. A coastal race is a small fraction of a megabyte, and a long offshore passage is still a small fraction of what the raw forecasts would be.
That is small enough to work on marina wifi or a metered satellite connection.
Pull the forecast once and you can keep computing against it: different departure times, wind scales, and changes to the course inside the same area, with nothing further to download.
Computing again is free
Once a forecast is downloaded, computing again returns immediately and spends nothing from your allowance. Change the departure, course, or routing constraints and run it again. The forecast detail is set automatically by your plan.