Light and fast hardman climbers will generally carry whatever is the absolute minimum they think they can get away with. There is an old adage in climbing that goes something like "Speed is safety. If you carry bivy gear, that just guarantees that you will need to bivouac!"

The Spaniard Kilian Jornet Bourgada just set a new record, climbing Denali and back down in less than 12 HOURS! The typical time is 17-21 DAYS.

Of course now and then that approach gets people into trouble.....