It may be mostly “security theater” but it requires almost no extra effort and drastically increases the difficulty of compromise by adding privilege escalation as another requirement to gaining root access.

It helps protect you because if the application in question is compromised in any way (or has a flaw, i.e. an accidental rm -rf /*), the only access it has is limited to the user it is run as. If it is run as root, it has full administrative privilege.