The most practical way to put it: a certification isn't buying depth, it's buying "knowing when to stop." You can get in the water without a freediving certification, but with one and without one, what's in your head is completely different โ a bit like a driver's license: it doesn't mean you drive well, but at least it proves you've learned the rules of the road and know where not to step on the gas.
What it actually gives you:
A set of safety procedures. How the buddy system is carried out, how to rotate one down and one up, how to do the surface protocol after surfacing, what LMC (loss of motor control) and BO (shallow-water blackout) look like, and how to bring someone back to the surface โ these are the parts of a course that are truly worth the money, not how pretty your finning looks.
A recognized qualification. Most dive shops, dive sites and liveaboards will ask to see a certification from a system such as AIDA/PADI/SSI when renting equipment or taking you to depth. Without a certification, in many places you can't even rent equipment.
A prerequisite for progressing. If you want to train to greater depth or follow the instructor path, the previous level's certification is a hard prerequisite โ you can't skip it.
But don't misunderstand: a certification does not represent the limit of your ability, and even less does it mean you can get in the water alone. It proves you have been trained and know the rules; how many meters you can dive depends on every practice session afterward with a buddy and a safety plan. If you only want to play around in a pool, a certification isn't that necessary; as soon as you plan to go into open water, it is the ticket in โ and, incidentally, one that can save a life.