When you discount your services, you are undercutting the value of the entire industry.  Ever bought a Groupon for a discounted exercise class, but then never went again for full price?  If you pay less for something it is really hard to fork over more money later.  When you lower the price of something, it sets a precedent and people don't want to pay more for it.  The perceived value goes down.  This may not matter when you are first starting or if you are in a slump and need whatever clients you can get, but it will matter when you are wanting to get paid more for your services or want to work on higher budgets.  It also matters to all the other designers out there working their butts off and growing their businesses.