There is a lot to be said for providing valuable content, skills or expertise online for free. Offering useful information demonstrates that you know what you are talking about, it helps to show people you can be trusted, and it gives you an opportunity to get your name ‘out there’.
It’s one of the reasons I make a freelance writing podcast – it helps to establish in potential clients’ minds that I’m knowledgeable and skilled in my field. Similarly, the writing I have volunteered for non-profit websites shows editors and clients my writing style and the topics I specialise in writing about. It has also increased my profile, all of which contributes to me getting work on a daily and weekly basis.
Giving stuff away for free is usually good; working for free is usually bad. Work out your limits
Giving things away is not the same as working for free – something that should, in most cases, be avoided at all costs. You don’t want to put yourself in a position where you are being exploited or taken advantage of. Instead, giving things away puts the power in your hands: you choose the information, or the value, that you will provide and you offer it openly. 
In this TEDx video, Simon Wheatley talks about how he got web design work from the likes of Stephen Fry and the Rolling Stones based on his reputation as someone who was “good at WordPress”. That reputation came from having developed plug-ins and contributed to the overall open source nature of the WordPress project. It’s a great talk to listen to and could provide some great ideas for freelancers who are considering adding more content to their sites or service offerings.
In the interests of full disclosure, Simon is my brother-in-law as well as being a top WordPress dude.