I think the type of clothing you wear makes a difference. If you dress with a hole in your shirt and stains on your clothing, you won't get as great of a service than someone who is dressed in a well-kept and appropriate manner. That is just how it is. First impressions are important so when you dress up nicely, people will respect you better. Now I am not saying that you need to wear a suit and tie everyday, just dress for the occasion or at least have clean/ well-kept clothes on. I think you should dress formally for a wedding or special occasion, it's respect factor. I will be honest, if someone came into my wedding with jeans and a normal t-shirt on, I would want them to either change or leave. Casual errands and hang-outs should involve casual clothes, special occasions or job interviews should involve formal wear. Saying at home or exercising? wear whatever the heck you want :P Let's say I was a boss and I had to hire one person for a job, Billy walks into the interview with jeans and a flannel t shirt, Joey walks in with a business casual suit and well kept hair? They both have an equal amount of good qualities but Joey took the time to dress better, which says A LOT.
I think its because people from time to time like to wear someone more out there or more classy. Wearing casual all the time gets boring. Plus I'm sure everyone wants to look nice. But hey of you want to wear casual go for it, I don't see anything wrong with that. I say wear what you want and feel comfortable in and don't do it for others, do it for yourself