Jails also have resource limits, so you can have a group of processes that are related, but not started from the same executable, be held to a certain amount of

Jails also have resource limits, so you can have a group of processes that are related, but not started from the same executable, be held to a certain amount of CPU, memory, etc usage. They're also useful in testing/debug situations; coupled with ZFS' copy on write features, they let you quickly create identical environments which can be real helpful in trouble isolation.