Allow us to disagree. Custom clothing is important. The reasons why are as clear and simple as ABC.
A is for Awareness. Awareness of your product, your organisation, your event. It's a great way of making sure that people know the reason you're around.
B is for Brand. We all have an item of clothing somewhere in our wardrobe that bears the logo of a manufacturer or designer. It makes you aware of the brand. It also helps with identification of staff in a store, restaurant or hotel. Has anyone ever asked you to find them something in a shop when you don't work there? Branded custom polos or t-shirts helps to avoid those embarrassing moments.
C is for Community. Custom clothing can help clubs and organisations to bond, to feel that they're part of something bigger. Look at the clothes that the T-Birds wear in Grease. Or the cool shirts ten-pin bowling teams wear. Custom clothing can help you show support for a cause or an idea, too. Look at the shirts that Fact Fashion put together raising awareness of third world poverty. Or Katherine Hammett's Choose Life shirts.
I think there are three great reasons for choosing custom clothing right there. If you need more, why not check out the Pier32 website? It's so easy. Tell 'em, Michael...