I can answer your question:

Imagine you decide to flee your country for whatever reason, but you lose your Trezor or decide not to cross a border with a gadget that shouts "I have some money here, please hassle me for bribes."

However, you have memorized your unique12 words from the standard BIP-39 word list. You are in luck! You cross the border, perhaps just with the shirt on your back, border guards none the wiser, arrive safely in your new home, and then you acquire another Trezor (or equivalent gadget).

Now you enter your12 words (AKA "seed recovery phrase") into the gadget and abracadabra, there's your life savings ready to spend.

The words are technically a human-memorable encoding of a random bitstring which forms the root secret key of a hierarchically-derived tree of secret/public keypairs, each of which should secure (ideally) a single transaction (ie. an inbound value transfer received by you).

Sort of like a just-add-water personal treasury. The gadget is only needed to spend or receive new value. The memorized 12 words represent (eventual and ideally exclusive) access to all of the value.

Hope that helps!