There's actually a fair amount of time spent on the taxiway by arriving planes waiting for gates. Sometimes they'll shutdown and wait, but often they're sitting

There's actually a fair amount of time spent on the taxiway by arriving planes waiting for gates. Sometimes they'll shutdown and wait, but often they're sitting there idling. That's a lot of fuel savings by reducing time spent waiting for gates. Additionally, increased turnaround times means that airlines can fly (on a marginal basis) more flights per plane per day. On high-load-factor routes that increased revenue can be significant.