Style guides are terse documents which have biographies, head shots, company name, company logo, and other key company data which is all there for marketers to see. This type of bare bones information about you and your company can make all the difference in launching a successful marketing effort and launching a confused or convoluted one.
One bonus a style guide offers is definite direction for your marketing departments partners to go when they are all coming to the table with their ideas. If you have a couple of disparate voices; a photographer, an events coordinator, a graphic artist or any other partner in the mix; and you all can't get on the same page about how to move forward with the marketing effort than the work suffers. It definitely takes longer; that much is for sure. So a style guide can be kind of an outline for all the different voices coming to the table and they can all see what your business is and what you want and don't want.
Style guides help your bottom line immensely. Imagine that you are getting ready to launch your next marketing effort and your graphic artist hasn't taken the hints you've gently laid down that your work does not go in the same direction as what they are doing. Your whole marketing effort is going to suffer. Moreover you are going to be delayed with all of the back and forth; you may even wind up having to sever chains with different marketing partners. Imagine if one of them introduced a concept which really began to dilute the brand you've built up and undermine your credibility. You don't want that to happen; you want all of your marketing efforts to be a success.
So make haste and get over to your marketing partner to find out if you indeed need a style guide. If one could help you, you should make haste and get yourself covered by one today!