When a service member separates from the military due to a medical discharge or retirement, the now Disabled Veteran and their family has to go out to establish a new life, usually faced with unfunded relocation, unemployment, and waiting on benefits from the Veterans Administration.
When the military sends people out of the service as a Disabled Veteran, the Veteran can incur thousands of dollars of debt in that time between the end of their military service and the time when they are employed, established, and settled into their new communities and lives.
When a service member signs to enlist, it is said they give a blank check to the country "in the amount of everything, including their life" to their country. If they are disabled in their service, pay that check.