Not sure about the designer part myself, but in the consultation agency where I work, we often do custom themes for clients. Installing wordpress and configuring it is easy enough, even for new developers - but getting them to understand the intricacies of theme development can be a bit tricky.
The themes included with wordpress, twenty-eleven and twenty-twelve can be too complex, and have a lot of cruft we don't need. So we usually start with a skeleton theme, like this one - although this one is a particularly well documented skeleton theme.
Sometimes it takes an example theme like this to make things 'click' for a new developer. For that reason alone, it can be very useful.
The themes included with wordpress, twenty-eleven and twenty-twelve can be too complex, and have a lot of cruft we don't need. So we usually start with a skeleton theme, like this one - although this one is a particularly well documented skeleton theme.
Sometimes it takes an example theme like this to make things 'click' for a new developer. For that reason alone, it can be very useful.