Being forced to sleep outside the camp walls was a part of the decimation punishment, though it had fallen out of use by the time of Crassus and Antony. After a unit had been decimated, the remaining members would be forced to camp outside, and were only given barley or fodder-grade wheat. It’s important to remember that decimation was a “punishment by lottery” and while one person was REALLY punished, it was the whole unit being disciplined. The forced outside camping would span the course of days.
The unit discipline would be given after a battle had been fought, or at some point in the relative safety of the encampment. The temporary banishment would not have likely endangered the soldiers, the point was to punish the men, not kill all of them. It wouldn’t do any good to have the entire cohort die.

The rations given were of a lower quality than what a legionnaire would normally be given, and would often cause gastrointestinal distresses. It’s also believed that the barley was viewed as a mark of incompetency, as new recruits were also given that until they demonstrated their ability to their superiors. After the battle of Cannae, some units were issued barley rations for seven years, but this doesn’t seem to be the norm The whole point of the exercise was to humiliate, shame, and further punish the disgraced unit.

Both of these punishments were very exceptional. Typical discipline involved flogging and fining. Decimation was reserved only for capital offenses.

Sources:

The Roman Soldier, George Ronald Watson; Cornell University Press, 1985

Roman Military Service, Sara Elise Phang; Cambridge University Press, 2008

Polybius, Histories, book 6, chapter 38

Titus Livius, Ab Urbe Condita, book 2, chapter 59