Flying with the wind always increases your ground-speed.

Time-distance/fuel remaining calculations begin shortly after take-off. Normally however, the winds at altitude are planned and if you are iffy on fuel remaining it's a no-go.

When the guys I work with need to take a plane to Hawaii, the question is whether Midway Island is open or are they going through Cold Bay, Alaska direct to Honolulu. The winds are very rarely adequate to support a direct flight from California to Hawaii.