Monitoring a meter, whether is be water or gas, gives the user 2 fundamental pieces of information:
1. It allows you to accurately determine the overall quantity of the water or gas being monitored over whatever period you are interested in. This could for example give you monthly consumption, which should tie in to your billing.
2. Alarms based on exceeding a threshold that you define over a certain period, and at a certain time of day. This could for example tell you whether you have leaks in the system. Determining this can save immense amounts of money by detecting problems when they happen, not when you get you next bill.