I think dressing well does give you a edge if you are working with the public. If you are in a corp. office setting and meeting with people their first impression of you will stay with them. I have worked in offices where there should have been dress codes because in Florida some of the people really took to looking like "I rather be at the beach than here". In other environments when one is working research or something that requires long hours, ect.... and they can get away with comfort-they should do it. Too me it is better to be neat than sloppy.
ITA that neat always wins over sloppy. If there isn't a dress code, stick with being pulled together a notch above your peers and you can't go wrong. You don't want to be known to your superiors as "the girl who wears those pink glittery flip flops with a bad pedicure and smacks gum all day."
In general, if you have a lot of client contact face to face you'll need to dress appropriately. Obviously, banking will be different from surfgear sales, for example
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As far as dressing sharp to climb the ladder, well as posted earlier if one's performance and ethics are kaput it doesn't matter how well they are dressed. I do think there is a balance between looking sharp and looking like you're trying too hard. It just depends on your work environment.
On a personal note, I'm in a business casual IT realm where I'm in my cube on the phone all day and in a few face to face meetings (internally with peers and mgmt). Many of my project teams are 'virtual,' spread around the country, so theoretically I could wear just about anything. During the week I stick with slacks or khakis. Jeans are fine too but I steer clear of hoodies and flip flops for sure. If I'm telecommuting or running an overnight conference call from home I'm often in my PJs!
When I travel for work, it's to visit other locations at this same company. There I DO dress more conservatively than I would at home, meaning avoiding jeans the first few days and bringing a nice jacket.
Sorry about the ramble..hope that helped?