If there is somehow an exploitable vulnerability in the program, if exploited after the tame call the attacker only takes control of a restricted process, which

If there is somehow an exploitable vulnerability in the program, if exploited after the tame call the attacker only takes control of a restricted process, which hopefully mitigate or blocks the attack. This a very smart application of the least privilege principle. The idea is that most programs don't need most syscalls after they complete their initialization, and thus dropping the privilege to use them is both cheap, safe and effective.