A file system is a map and a territory. The map is the tables at the start of the card, the allocation table or bitmap and the directory entries, and the territory is the data area behind them where the photographs and video actually sit. A quick format throws away the map and draws a blank one; it writes a few kilobytes at the start of the card and touches nothing in the territory. The SD Association, which publishes the formatter most makers recommend, says in its manual that the data still remains in the card after a quick format and may be retrieved with a recovery tool, and the bench retrieves it by reading the territory directly, carving each photograph out by its own signature and giving it back its date from the metadata inside it.
A full format is different in kind. Microsoft's documentation records that from Windows Vista onward the format command writes zeros to the whole disk when a full format is performed, and the SD Association's formatter offers an overwrite format that erases all data by overwriting the user data area completely. After either, the territory is gone and no laboratory recovers it. The box in the Windows dialogue is labelled Quick Format and is ticked by default; a format run with it unticked is the full one. Cameras' format functions are quick ones on nearly every body, and a few offer a deeper option under a name such as low-level format; what each body's deeper option writes is not something to find out on a card with the pictures on it, and the free look reads what is left before anything is promised.
Deleting is gentler still. In camera or on a computer, a delete marks the file's entry as free and leaves the data where it was; on a card there is no recycle bin, so the entry is marked at once, but nothing is overwritten until a new file needs the space. That is the whole of the rule: the first new photograph after a delete or a quick format is written into the freed space, and it is written over whatever was there. A card that was formatted and put away comes back nearly whole. A card that was formatted and shot on for a week comes back with the week's photographs and whatever the week did not reach.
Recovery software does this job well on a card that reads cleanly at its right size, and the software page says how to do it safely, on an image rather than the card. The bench is for the cards that do not read cleanly, for video that comes back without its index, for RAW formats a tool does not know, and for people who would rather the first attempt were the right one.