The benefit of water tests is that you know specifically when something is out of range. Try to avoid the tendency to not test because you might not like the results. Instead, use those test kits frequently, and track the data to watch how the water trends over time. If a kit can be used 50 times, that means it will last you a year. The expiration date is a clue that it won't last forever.
Water tests are performed often. Specific key areas may be checked or tested daily or every few days, but the full battery of tests are done once or twice a month. When those are completed, that is when I update my spreadsheet and post it on the site.
For more information about testing and maintaining stable water parameters, refer to this article: http://www.reefaddicts.com/content.php/302-Maintaining-Good-Water-Quality
Below are the basic parameters within acceptable range limits, but a tighter swing within the high and low range is best. For example, if pH measures 8.1 to 8.3 daily, that would be better than 7.9 to 8.4 daily. The more consistent with limited variation, the better.