What is the point of FileVault on a Mac with the T2 security chip if the chip is already responsible for encrypting the drive?

Does having a Mac with a T2 chip automatically prevent someone from booting into Recovery mode or Target Disk Mode or from accessing disk utility or a terminal without having a user's password credential? Finally, are there any stipulations associated with having FileVault turned on or off on Mac with the T2 chip, with respect to booting the device into something like Target Disk Mode?