In a word; service. If you know exactly what you want, and can pick it out at that store, and are prepared to stay at home supervising your remodeling project, then the installed sales (I.S. as they are called) department at the big handyman stores might be the way to go. Typically, the quality of installation, and attention to detail is not an I.S. trademark. Neither is custom or out of the ordinary work. A lot of things 'pop up' during a remodeling project. Unforseen damage or conditions are a daily occurance. A remodeling company usually has the people to deal with these 'things' in a timely manner, and keep things moving. A remodeling company has greater flexibility to get the job done. Usually, the big handyman stores do not have the high quality materials that people often are wanting. In fact, manufactures will make lower quality products to sell to the big handyman stores, then those they sell to plumbers and remodelers. An apple is not always an apple when you buy from the big stores. Like most things, there are situations when a big box store might be the right way to go, and there are times when it is best to have a professional handle the COMPLETE job. Every situation is different, but carefully compare estimates from each of these types of companies. Is it an apple to apple comparision? Usually not. Buyer Beware.