Of course none are necessary, but the question was how USEFUL do you find them.
I love Runkeeper for keeping track of my runs and calories burned. The Weather Channel app is great, too. I don't watch a lot of TV and my local news station's website is difficult to manage, so the weather app makes it easier for me to plan activities, such as pool and park, with the boys. I also like My Fitness Pal for keeping track of calorie intake and workouts. Not necessary, but it's something I enjoy and helps me feel a sense of accomplishment. I also like the Kindle app on my phone for reading sometimes when I'm in bed and can't fall asleep. I own some poetry books on the Kindle and I enjoy reading them and winding down before bed.
The battery does run down easily and that is a downfall. I am almost never without a charger.
I do like the Weather Channel app.
I will have to try runkeeper, thanks :)