There are 2 answers to this question.
1: to become familiar with the area and to know the hydrants are in working order and their flow rates, and
2: as part of the North Carolina Response Rating Schedule (NCRRS), which determines your insurance rating, there are certain criteria we have to meet, and one of those is hydrant maintenance. Our Hydrant Maintenance Program consists of flowing and flushing hydrants 2 times a year, and we have set months established for this. If there are any immediate concerns, we address them accordingly, and we are always mindful of environmental conditions such as droughts and modify our program if needed. Caution is taken during the flowing of hydrants so as to not disturb surrounding landscaping or cause traffic hazards.
Side note: the colored bands on the fire hydrants let fire personnel know the flow rate (depending upon the color) and the hydrant's ID number is for referencing in our system.