Just my experience, but here's what a web site actually does for you in most instances:
- It will lend credibility to you (or your company) if it is not too generic. If the site looks like a template or just some random stock photo infused script, it won't help as much as it will hurt. It needs to be personable and unique.
- It may provide uncertain clients a place to view your work.
- It may help past (or existing) clients find you if they've lost your contact info.
- It provides you server space so you can send clients link to items they need. (It looks more professional, in my opinion, if you use your own domain rather than drop box or hightail, etc.)
That's about it.
Now, if you want to invest a whole bunch of time into beefing up a site with tech blogs and articles, etc. then you may be able to swing in some ad revenue if traffic increases enough. But that can be a lot of work for little return unless you build a go-to site that is very unique. Realize in this day and age any new site is going to struggle against sites that have been around for a decade unless there's a very unique pull. And (as morsor answered) who do you target? Clients? Other professionals? You won't get work from other professionals and there's just so much client-focused content you can create before a site just looks like an ad-revenue site, and thus unappealing to clients.
One thing my experience has shown me is that my web site has never gotten me any work. At best, I'll get a contact form submission from some random person wanting a quote without providing any information and when asked for more info, they don't have any. So, essentially wasting my time. I haven't updated my web site in about 8 years. Yes it needs an update. However, it still appears fairly modern and is still very functional, so updating it hasn't been a pressing matter. I have too much paying work to worry about my own web site. In fact, I've considered hiring someone to update my own web site because it's such a low priority for me.
Make no mistake, a web site is must. And it has to be functional and appealing. But I just don't feel mine has ever pulled in any client. I get clients 95% of the time via word-of-mouth. (I've never used any freelance marketing website).
The competition online for an online business is rough. Just imagine trying to compete with eBay or Amazon... well that's essentially what any "web development" site is going to do... but worse since web dev is web dev and SEO, tricks of the trade, etc., are known by all the top competing businesses in the field. Coming to the game late (2016/17) just means there's ground you'll never make up unless you have a team of dedicated workers all striving to overcome existing top-ranked search results.
In short, forget about trying to compete online. Just make a nice web site.. then focus your marketing efforts elsewhere.