Drought conditions stressing lawns and gardens.
Or, for some people, it is just not practical to water a large lawn, particularly if they do not have a lawn irrigation system installed.
Cool-season grasses.
In most years, lack of watering is not a problem, but when no rain falls for several weeks in a row, permanent damage can occur to cool-season grass lawns.
Mower height adjustment.
It is OK to leave the clippings fall on the lawn, particularly if you use a mulching mower.
Then, that root zone should be allowed to dry out somewhat before you water again.
This tends to keep the very top of the soil profile saturated which discourages root growth down deeper in the soil and also excludes oxygen from the upper layer of the soil which leads to thatch accumulation and potentially disease problems later on.
Then, when the soil dries out, turn it on and it will water just along the row and not the whole garden.
Placing the ooze hoses or drip lines beneath mulch also helps further reduce water loss by shading the soil and reducing evaporation.