First of all it's important to understand that any given song can only have one publisher that represents it at a given time. It's either going to be you, or it's going to be a third party in the event that you sign away your publishing rights to someone else.
A lot of writers are understandably reluctant to sign exclusive contracts with publishers. I can understand and relate to this reluctance, but to fully appreciate the issue it's important to consider the point of view and the role of the music publisher in the context of music licensing.
Music publishers make their living by developing relationships with music supervisors, ad agencies and the like, as well as the songwriters whose music they represent. Based on my own recent personal experiences with my new music marketing company I can assure you that this is very hard and competitive work. In order for successful music publishing companies to make a name for themselves, they like to have a unique catalog to present to the licensing community. If all catalogs were the same there would be no incentive for someone to do business with one publisher vs another.
The analogy I often make is that it's similar to the way music retailers operate with the manufacturers they represent. There are geographic restrictions that allow music retailers to carry instruments and equipment that can't be found within a certain proximity to a retailer's location. It's the same principle at work. If you could simply walk into any one of a dozen stores in the same town and find the exact same type of gear there would be little incentive to do business with one store over another and retailers would have much less leverage in the marketplace.
So the question remains. Should you or shouldn't you sign exclusive contracts? I always advise writers to assess several factors when making a decision. First of all, what other offers do you have on the table? And secondly, if you are offered an exclusive contract, what is the track record of the company that is offering you the deal? Are they a fairly new company with few credits or are they an established company with a verifiable track record of placing music in TV, Film, etc.? If the latter is the case it would probably make sense to take a chance and sign a couple of your songs. You can always negotiate for a contract that releases the publishing rights back to you after a finite period of time. For example, one to two years. Also keep in mind that if you are a prolific writer, and you should be if you're pursuing licensing opportunities you will always be writing new material that you can place with other companies as well.
Over a year ago I created a one of a kind program that teaches musicians, in a step by step fashion, how to license their music for use in TV, Films and even Video Games. This program took me several months to develop and is based on my own personal experiences of licensing my own music for the last six years. My program is called The A-Z Of Music Licensing and it includes EVERYTHING you need to know to begin the process of successfully licensing your music. It even includes a directory of contact information for the music licensing industry so you'll know who to contact. The program is a digital product that contains both an audio and PDF portion. I also offer the program with additional email coaching if you feel like you need extra support in getting started. My service, to the best of my knowledge, is the only service of its kind for musicians interested in entering into this exciting business.