Personality Reboots were a way to protect the psyche of a soldier during the War.
A copy of a soldier's personality was downloaded and embedded in an item or body part. Should the rigours of time travel and combat lead to a potential mental collapse, the backup could be uploaded to correct the damage. This could cause lost memories but was better than the alternative. However, it was mostly used by the lesser species and not the Homeworlders running the campaigns.
The concept was developed further by the Celestis, who used it to make their worldofme devices. (PROSE: The Book of the War)