Even if it’s signed software, the sandbox is a useful layer in limiting the scope of any vulnerabilities it has. Say a media player has a bug in its decoder tha

Even if it’s signed software, the sandbox is a useful layer in limiting the scope of any vulnerabilities it has. Say a media player has a bug in its decoder that allows a malicious video file to make the player execute arbitrary code. If the program is sandboxed, they shouldn’t be able to pivot from that into stealing your ssh keys or recording your screen.