The superuser can modify the shells of other users, by supplying the name of the user whose shell is to be modified as a command-line argument.
It can also signify a layman with only user account privileges, as opposed to a power user or administrator, who have knowledge of, and access to, superuser accounts.
This is valuable, since if the system administrator did not intend for a second superuser account, then it may mean that the system has been compromised.
Setting the clock is restricted to the superuser.
Many exploits are designed to provide superuser-level access to a computer system.
Only the directory owner and superuser are exempt from this.
Superuser status is conferred on users who have been selected by foursquare staff for their helpful contributions to the community.
Even if the attacker gained access to the jail's superuser account, he/she could only modify that jail, and not the whole system.
