There are many companies that put this approach into practice. I believe that there are many reasons to hire a company that puts IMC to your advantage. The main reason to hire a company like this is so that all of your outgoing messages between different media are consistent throughout. Having a consistent message going to your public is very important. A company would not like to send out three competing messages that communicate several messages to their customers. By having a succinct approach and communicating one message to your customers will only help your business and help customers return for more than one purchase.
IMC is a great thing for any company. Putting IMC into practice will only benefit your company. Having the company's marketing, promotion, advertising and public relations done all at once by one company is why IMC is the way to be.