It depends on your threat model. The OP mentions bobby traps and self-destruction, so I assume the threat model here is not a typical model in personal computing, but a different one, which is similar to Dread Pirate Roberts' threat model, as explained below.

Self destruction has two advantages, comparing to shutting down the system. First, once the encrypted master key in the header has been wiped, the data is gone, it's technically impossible to recover the data anymore (your passphrase is only the key to decrypt the master key in the header). On the other hand, revealing the passphrase under pressure is always a possibility. Second, when an attacker tries to seize your system, a possible strategy is seizing your system alive in a surprise attack, giving you no chance to shut the system down, and using an USB mouse emulator to defeat the screenlock.

And the reason of using a hardware-backed key storage, is to prevent the clone of the encryption header (which makes the self-destruction useless), and to ensure the destruction of the key is complete. In modern SSDs, due to wear levelling, there's no guarantee that the physical sector the header belongs to is actually erased.