I may be the one who talks most about breeding fish. When I get a fish, it's usually because I've researched about it. Most of my fish would be considered rare in the hobby, and that would make them expensive and hard to find, if I hadn't developed a network over my many years in the hobby.
So if I get a fish I like that only lives 2 or 3 years, I will soon either say I used to have it, or breed it and continue to enjoy it generation after generation.
If it is very expensive, but I know it's a social creature, can I always afford 10 $25 uncommon "new" tetras? Nope. I'm retired. Can I "make up" a group with a little learning and a little work? Maybe. It's always worth a try. Maybe I can afford a couple of females and a male or two. Then, I can have a lovely shoal within a few months, if I'm willing to work at it.
There's something satisfying about looking at a shoal of (inexpensive but stunning) cardinal tetras moving across the base of a tank, and knowing some of them began their lives in a fishtank in my place last winter.
I have a 40 gallon paludarium variation tank with no fish in it but Chromaphyosemion poliaki. When I got them, 20 years ago, these 3 year lifespan fish were a very commonly imported killie. In the small world of killiekeepers, they drew some snobby reactions when I talked about them. They were common killies. They usually came in Cameroon shipments then.
Then the mountain they lived on was developed for one of my other great loves, coffee. The forest with its cooling canopy was gone. C. poliaki became a threatened species on the IUCN red list, and is apparently even worse off now than it was when that was assessed over a decade ago. I can't save a species, as my lifespan as a human is far less than that of a species. But I breed them, and maybe a dozen other people have gotten them from me and liked them enough to breed them too. If the fish keeps spreading in the hobby, maybe future generations will at least be able to see it.
Without breeding in tanks (combined with habitat preservation that isn't happening), it would just be a few old photos to us.
Plus, you watch a fish swim. Then it swims more, After that, it swims. Take a tetra, for example. Many people say they're boring. But try breeding one. It'll keep you busy, make you think and maybe defeat your attempts. It becomes a puzzle, and a challenge. There's great satisfaction if you succeed in breeding it and raising a group to adulthood. Then you can start again, with an active hobby. It's like buying bouquets of flowers versus gardening.
So, there's cheapness. If you want 50 tetras, buy 10 and give it a go.
There's rarity - there are a lot of aquarium species that have gone from the hobby, and some have become extinct. You can't wish them back.
There's really learning. I keep a killie collected by some French guys in 1989. It's beautiful. I acquired some in 1992, and was told I was too inexperienced to succeed with them. I worked at it, and learned with them. I still have that line, a favourite fish that is older (as a breeding line) than my adult children are.
Several attempts to find it again in the Republic of Congo failed. Its habitat is now a palm oil plantation. But in 2022, some other French guys found a way into a narrow ravine with a Spring fed brook. It's a tiny microhabitat surrounded by a mega farm that finds it useless because it's too steep and hard to access. They found my fish for the first time in 33 years, and I now have young from their collection in a 10 gallon. Yesterday, I saw the first hint of colour in a dorsal - I have at least one male. Will my breeding stock have changed their appearance in captivity?
I'll soon know. I'll breed them as a separate line, without mixing them, and see if they are as difficult as I found the 1992 ones. Maybe it was me, not knowing how they worked that was the reason for the trouble. I'd like to know that.
My original pair died in 1994, and by now, I would have forgotten a lot of details had I not bred them. I've had a lot of fun with that fish since then.
I keep lousy records and am not a list keeper. But I have a plaque from the breeder's award in my local club that says I'd submitted forms for 90 fish by 2009. I recall having about 30 more done and filled in that I didn't bother to take in, and I've bred about 5-10 new species a year since then. I figure I've bred around 200 species, and I have learned something I've enjoyed learning with every one. Just looking at them wouldn't be as satisfying.
So yeah. When you can get the time and resources, try it!