Earlier quoted context omitted.
These devices allow you to perform a brute force attack. Jailbreak requires a reboot of the device and after a reboot the encryption key for the useful data on the device is not available. If the device uses a strong passcode (as opposed to a numeric code) it cannot practically be brute forced even if you force the device to allow you to enter many attempts quickly.
This is exactly why I use an XKCD style multi-word password for my phone. TouchID/FaceID keep me from having to enter it a lot and the rapid pressing of the power button to disable it give me convenience without significant compromise.
70^8 = 576480100000000 // 8 chars of upper/lower case, numbers, symbols
4000^4 = 256000000000000 // 4 words pulled from a vocabulary of 4000 words
word rank
------------- ----
correct 1808
horse 1286
battery 3221
staple (not in the first 4000)
https://xkcd.com/936/ (For those who were wondering about the context.)