I recently read this blog post and found it remarkably insightful!
In short summary, there is an incredible number of on-line spaces where you may want a presence, and they’re growing by the day. Every space you occupy needs it’s own specific type of design, planning & interaction. Beyond a point, it’s tough & expensive to manage, probably requiring dedicated personal/software or an agency. An alternative is to setup all your profiles, but keep the content on your own website – so as to drive the traffic back to your main website (where your conversions & tracking happen anyway). Leaving you (effectively) with only one channel to manage.
If you don’t have the extra time (or software) to manage multiple channels, Seth’s approach may be easier – though it might lack the depth of engagement you can achieve with the extra time and more micro-management.