Water testing-- at this point I don't normally test very often, I'm confident enough in what goes on in my tanks, and it's zero ammonia, zero nitrite, low nitrates, and pH settling at 7.4 after big water changes (well water out of the tap at 6.4-.6.6). Occasionally I'll add Seachem pH and ammonia monitors to the tank, normally when I've changed something significant or for some other reason I want to keep an eye on things for a while. As a sanity check I test nitrates now and then (they're low). I was testing pH with each water change when I used to alter chemistry for the sake of higher pH fish (or, before that and decades ago, when I did low pH blackwater tanks), But I wouldn't be without test kits, because at any sign of trouble the first thing I do is test the water to know what's going on and (presumably) eliminate water conditions as the issue. For me that's fundamental.
Otherwise, I come from a perspective that sometimes what seems unconventional can work and if it works it works. It goes back to the 1970s when a friend left for college, left his tank for family to watch over and they never fed the fish or changed water, yet he came back in three years to find the tank had settled into its own little ecosystem, tons of algae but still had fish in it, apparently eating algae and fry (I forget what kind of fish in the tank). Doesn't mean I'd ever do that, but if someone does something different and it works for them that's fine by me, a centuries-long history of fishkeeping, most of it before modern equipment, has seen more than one method. What does annoy me are the guys (like Father Fish) who think they've reinvented the wheel and want to convert everyone else, making loud claims like YOU'RE DOING IT WRONG! or STOP DOING WATER CHANGES! No I'm not doing it wrong, it's worked quite well for decades, my personal criteria being having long lived fish, plenty of breeding success when that's been the goal, and very rarely ever dealing with health issues.