Businesses get a unique advertising opportunity and people (and dogs*) get a free t-shirt. Check them out.
*Gitchers even lets people request t-shirts for their dogs.
Implications - People love getting free things, even if it is something little. A business that gives away its items or services in samples exemplifies a great way to gain public attention. Often times, people will try a sample, realize they like it and will buy the product or service when the free sample runs out.