In comparison to reactive testing , proactive maintenance and dosing have given me better results at a fraction of the cost,time and effort/loss of enjoyment.
To balance my post a little bit, let me say that if you ever used a thermometer to check the water temperature of your tank ... you tested your water. Used a pH test (liquid or probe) to figure the 1pH drop for your CO2 injection? You tested the water.
In my opinion, the most important point that was made is that most hobbyists become very absorbed by the numbers they get and forget to look at the tank. For example, how many starting aquarists we know who are adding chemical to get the exact pH found on some website . How many are guided in their decision to do / or skip water changes purely on the nitrate test kit result. Following that logic adding a nitrate removing solution such as a selective resin = never change water. Many times the issue is caused by something that was never tested for or can't be tested for by the average aquarist ( 'liquid carbon' cytotoxic effects etc.).
I agree with the previous posts that highlight the issues with test kits for nutrients. Some are better than others, some are unreliable even for yes/no results, some have gotten better/cheaper over time. As was mentioned, even if equipped with recently calibrated research grade gear the person doing the test is just as important. Just ask your newest intern to test a sample and give them the same samples to test after 6 months of learning

In that sense, testing is not a required skill to be an aquarist. I test nutrients when I experiment, normal tanks I just enjoy.