Personally, projects that you have started working on for a client and then they cut the cord, should probably remain in your personal reservoir of code to pull from at a later date. However, when it comes to IP you should most certainly share your ideas with the world. I suppose this revolves around the number of projects you have completed. If you are newer then by all means use everything you have. You’ve got to show something right?
The link that CodeGraphics shared was not a project that a client aborted. It appears to be a project that the owner, who in this case was also the developer cancelled due to a number of reasons. In this case I think he has all the right and should share his own IP. Pretty cool if you ask me. It’s a shame he did away with it. I understand his reasoning for canceling the project though.
Although, even if you have one solid portfolio piece, it’s good enough to land great clients. Because, it’s not necessarily about the design. Clients that may contact you see a level of competence, most of them have no idea what good design is, so if you received an inquiry there’s already some interest. Your job is to communicate your value and hold your clients hand throughout the process.
It also depends on what type of services you provide, if you are building themes and one-fits-all solutions, then sure reuse the design, repackaged it, show it… but if you create custom solutions that incorporate clients research, branding and etc., then IMO you should keep that work private and use it as resource.
A lot of beginners feel the need to show volume, and I advise to do the opposite. Now if you are looking for agency work showing experimentation/incomplete work and where you made mistakes can actually get you a job, most employers walked in your shoes once before.