In traditional and ancient cheese making, modern culturing techniques such as frozen mother cultures or freeze-dried DVI cultures weren't available. Without realizing what they were, cheese makers had to make use of the natural, endemic LAB cultures that naturally populated the dairy animals' teat canals.
They had to strengthen and feed those cultures to make them strong and dominant to exclude pathogenic cultures. The strong cultures would find a balance among themselves and mutually benefit each other.
Some may have used and developed clabber to help ensure a cheese batch went well, but many just used the same whey bucket, with a little leftover whey from the previous cheese making session (hopefully only one or two days old), and put the current day's milk into it. The cultured whey would populate the milk, acidify it, and the next cheese making session was rolling forward.
Culturing today's cheese from yesterday's whey is referred to as whey backslopping, and traditional cheese makers discovered this helped them make relatively consistent cheese, so long as they made it regularly.
Whey backslopping should be considered an advanced technique, not one for beginners, and not one for cheese makers who are not regularly making cheese (multiple times per week).
This technique still requires cleanliness and care, where it's important to not allow the whey to become contaminated. If the whey is refrigerated for a long time, it may change the balance of cultures, and may need to be fed a couple of times at room temperature or at thermophilic temperature (110 F) to strengthen it.
The idea that a cheese maker can just not bother cleaning his or her whey bucket and dump each day's milk in is not correct. The propagating whey culture needs to be cared for and fed regularly, the same as other natural cultures like kefir, yogurt, sourdough starters, and so on. Also, the dose (amount of whey compared to the amount of milk) can affect how fast the cheese acidifies, and this will require some attention and measurement to determine how much whey to reserve for the next day's cheese.
Note also that in traditional cheese making history, there were plenty of times where things went wrong and the cheese became inedible, contaminated, and made people sick. The modern understanding of how cultures work enables safety and consistency improvements even to whey backslopping, but cheese makers should understand that there is a different risk profile to this technique than when using other culturing methods.