: As a professional graphic designer I should encourage people to hire professional designers, and there are certainly* advantages to that. First off: You are dealing with an actual person/people

@Sims2060225

As a professional graphic designer I should encourage people to hire professional designers, and there are certainly* advantages to that. First off:

You are dealing with an actual person/people rather than a website that mediates all interactions between you and the designer(s). I personally dislike phone calls and prefer e-mail, but sometimes a phone call or face-to-face meeting is just the best way to communicate quickly and efficiently with a client (at least at the early stages of a project)
You are restricted (at least in the case of 99designs) to running specific contest-types and have less freedom to contract custom design packages. Brand identity is more than just a logo or a business card, and being able to work with a single designer to create your entire brand strategy is a huge advantage. Plus, you can build a relationship and rapport with the designer or design firm. This yields opportunities for further collaboration with a designer that is familiar with your business needs.
You are working with quite a different level of designer. The majority of crowd-sourcing designers are not experienced or professionally trained.

*That said, there are some major caveats to the above:

Graphic design is not easy to comparison shop for for most clients.

Design quality is not easily quantifiable, so it's hard for clients to look at 2 designs and 2 rates and determine which is the better value.
Most clients don't have the connections or knowledge to find a large pool of designers to compare. Instead, most just look at the 2-3 local designers in their area or go with the first designer they come across (usually sticking with them forever).
Graphic design, especially web design, is an over-saturated market full of under-qualified and untalented "professionals" who've simply taken a Photoshop class at their local JC and then decided they want to be a designer because it's easy money.

As a corollary of the above, design success has more to do with connections than ability. Most clients have very low standards/expectations (for the above reasons). So almost any designer will be received with open arms and recommended to other business owners. So going on professional reputation will almost guarantee overpaying for a mediocre design.
Crowd-sourcing therefore lets you cast a wider net and not be restricted by your geographical location. This may not be an issue if you live in San Francisco where there are artsy/creative people everywhere, but if you live in an average suburb or small city, you will almost certainly want to look elsewhere for design talent.
Because professional reputation means very little in most cases, it's almost better to crowd-source young high school or college students who don't have the ego to charge you 0/hr for a simple logo design. And crowd-sourcing by nature eliminates any personal bias based on age/gender/social skills/experience. All you really have to go on are results.
If you really need the one-on-one attention of a human-being, you can always swap numbers with the designer(s) you find on a crowd-sourcing site. But chances are, you can give them the necessary feedback over the web.
It is almost better for the client to have minimal involvement/delayed feedback when it comes to design work. You're hiring a good designer mainly for their aesthetic eye, not just their ability to use a graphics program. Let them do their thing and pump out a set of designs for you to choose from, then through repetition you can refine the design until it's something you're both happy with. Clients who get too hands-on often preclude a good design. It's like having a concert attendee direct an orchestra, or making the designer work with one hand tied behind his back.

So as a designer, I prefer clients not to crowd source their design work. But as a consultant, I have to acknowledge that crowd sourcing makes the most business and financial sense in 95% of the cases for small to medium-sized businesses.

However, if you have greater business aspirations (i.e. you want to become a 37Signals or YouTube instead of just a moderately successful web company, or you want to attract enterprise level clients to your business rather than just small accounts), then you will need to think bigger. Then it might make sense to shell out a little more and hire a professional brand consultant, as branding is a major component of a comprehensive marketing strategy. But this only applies to that rare 5%.