It seemed to take current conditions into account - route around areas that are already bad but it didn’t seem to account for typical volume at the time you’ll likely be somewhere. We used to get these routes showing normal speeds all the way through NYC, even though it was obvious that conditions would be different by the time we go there.

I’d hope they’ve improved it since then. I mostly stopped using it because I’d get tons of unprotected left turns on major roads or zig-zag routes through neighborhoods and it just wasn’t worth having to deal with that to save a minute.