Why have house styles?
Good marketing demands that a company uses similar styles in all printed material. People immediately recognise well-known brands because the logo, colours and typefaces are always the same. Companies should have their own house style manual. It doesn’t need to be particularly big – often a couple of pages are sufficient – especially if you refer to a standard manual (like the Australian Government Style Manual published by John Wiley & Sons). However, your house style must cover some specific elements like colours (especially in your logo), and typefaces. Professional graphic designers know how to deal with these, and can make recommendations.