if i go into philly for the day, i wear one of those and put my phone accessories(extra battery, charger, headphones) etc, beats carrying them around in your pocket, and yes i need extra batteries with my android phone...can also carry a bottle of water or something. it's just convenient, i've given up worrying what i look like to others
keep in mind i am taking light rail into philly so i can't just keep things in my car and go get them when i need them, if i go into the city, i am gone for 8-10 hours.