As happens so often with garden advice, it doesn't take into account all growing conditions. The myth about water scorching leaves is not a myth here in the Southwest. I can assure you that overhead watering of roses WILL scorch the leaves. Other plants don't seem affected. Also, it is perfectly acceptable, even desirable to water at night here. The plants get more of the moisture and are ready to face the heat of the next day. Difference in growing conditions is why, when asked for garden advice, I almost always start with, "Depends."
Absolutely agree with dahlmarye! If you'll water your plants overhead in 104 F in sun after 10 am in Texas (I am talking about North Texas) - leaves will scorch. The best results I had is to water plants after sunset.
I've not had leaf scorch from watering during the day in TX. Of course I'm more interested in watering the soil than the leaves, but the leaves do still get wet. But I disagree that it's not good to water at night. It rains at night, doesn't it? Do most plants get fungal diseases or whatever every time Mother Nature decides to rain at night? I think not.
I agree with tx flower child. Hard to tell Mother Nature to hold back that thunderstorm til early the next morning. Here in Pa, they usually dump their loads of rain in late afternoon, evening, or nighttime. Long before man worried about fungal disease, Nature took care of her plants in this way. Should they not have evolved to combat the disease...or died off due to their weakness? There are no pampered plants in the wild.