With multiple tanks, after few years I set only several times in year. But taking a close look at tank and its inhabitants behavior at least twice a day.

• With ammonia spike, they become agitated and trying to leave the disaster area. Having Seachem Ammonia Alert in the tank and actually looking on it at the feeding could help, but it can only show that there is toxic ammonia, not to do anything about it by itself.
• Nitrites should follow ammonia spike, keep an eye on them after that.
• The rise of nitrates can be observed by the tank state, it is not as pristine as it was. Similar to how 100 yrs old abandoned front yard is different from a manicured lawn.
• KH down to zero or pH swings: diseases and unexplained deaths. When it was not you who removed it by yourself, read about old tank syndrome, acidity part. Can happen with fairly new tanks too.
• Toxins: unexplained deaths. No testing for this, dealing with consequences.
• Noxious bacteria and microorganisms taking over the tank, with too much uneaten food left to rot in the tank, especially in the summer heat weave: as with a person, who is not well and obviously needs medical attention. Described as lethargic for shrimp. Start cleaning and water changes. I also used Lowkeys Recovers (fucoidan) and, later, cheaper peroxide treatment by MarksShrimpTanks procedure. Was safe for berried shrimp and their babies.

There is a one fine point with testing: it only shows if something is wrong, one of so many parameters that can't be tested, because there is no hobbyists tests for them. And it does not replace actions for keeping tank at its best, and not relieves a disaster. Testing frequently makes sense early in the beginning, when getting familiar with this. Later it's more for entertainment purposes, if you have a lot of free time on your hands, to get a feeling that you did something for your tank, without actually doing any menial work. It could be spent on keeping tank in a better shape or learning about how it is done.