I will admit that between mid-May and early October in Phoenix that displaying weather on my phone is redundant. Living here between those months it will be 100ºF at a minimum every day. The only change would be in late July early August when there is sometimes rain.I'm surprised when some people have it in like 5 different places but it's definitely useful to have here. In the next 7 days we go from -40 to -2, then back down to -20 Celsius (-40, 28, -4 F).
Looking outside is great but when it's -40 it's usually really sunny and looks great outside. A little warmer is usually cloudy or snowing.
It's a lot easier though to look at my phone then get off my lazy butt and look outside.
Especially though since I'm no forecaster and based on what I see outside would dress appropriately only to find out that the nice sunny weather turned to cold rain later in the day and I had no coat.