The time de-fibrilating re-bustler was a device to stop the TARDIS from being bigger on the inside than the outside by disabling its dimensional transcendentalism. Therefore the Eleventh Doctor also called it the "if you press this, the TARDIS will stop being bigger on the inside than the outside and crush us in 40 seconds switch".
Someday in the 29th century Amy Pond accidentally hit the time de-fibrilating re-bustler. The Doctor had to reconfigure the binaries, but his sonic screwdriver was broken and he needed to put it together again within 30 seconds and then he only had another five seconds to repair the TARDIS. When he was finished he told Amy to presses the time-defibrilating-rebustler to reset the system. Amy did so and the Doctor and Amy were saved from an otherwise certain death. (GAME: Evacuation Earth)