I once heard that 9 out of 10 complaints to the water company can be traced back to leaky toilets. Personally, I’ve had experience with high water bills and water damage, neither of which are fun, not to mention how expensive they can get.
It’s a good idea to do your own quick and easy test every few months, and when I say “easy,” I mean EASY! Just take the lid off your tank and put a few drops of food coloring in the water. Wait at least 30 minutes, then go look in the toilet bowl. If you see ANY color in your bowl, you’ve got a leak somewhere and it’s time to call a plumber.