Water quality is important if you have a sick fish because a lot of fish health issues are actually caused by poor water quality (ammonia, nitrite, nitrate or wrong pH). So if you get a sick fish, then we ask for the water test results so we can rule out any water quality issues.I have one cycled tank and another in the cycling process. Also, I get asked a lot on here about my water parameters, so I do need to know what they are to the full amount.
The same deal with new tanks that are cycling (developing the beneficial filter bacteria). We ask about water test results to see how far along you are in the cycling process.
If you can't afford the liquid test kits, then go for the paper ones. They aren't as accurate but do give reasonable results that are close enough for most purposes.