Why split Bitcoin backup 24 seed words into two parts (words 1-12 + 13-24), & store in separate locations?
This eliminates the risk of catastrophic loss that could occur if all 24 words are kept together.
24 seed words = 256-bit security
12 seed words = 128-bit security
or...
Using seed words + passphrase, offers superior two-factor security than just splitting seed words.
The advantage is that each separated part can also open valid Bitcoin wallets (with a few sacrificial sats), hiding the very existence of hidden wallets.