IT depends on the following.
If you are a fresh graduate, projects in academics and aside are very valuable because they are the primary factor your insight while you still had no opportunity to face real world. But it truly depends on the depth of the project.
Even if you are graduated and yet to find a job (this happens quite often in some countries) and you show Additional project, it applies as above for evaluation and on top of it, it backs your claim I wants to constantly learn
If you are continuously employed, sometimes additional project is a great way to show capabilities you have otherwise learnt. For example, you want to switch to new technologies, but if you don't get opportunity in your current employment, additional project is a great way to tell your new potential employer that you are already learnt these things on your own and you are so keen that it will worth the employers' investment to grow with these area.
But, if you have a deep gap in employment and just to show that you were busy - it will never give you at par rating as much as doing things on the job. This definitely is significantly dependent on quality and depth of the work.
Don't only do it - seek evaluation
University projects gets evaluation grades, and company projects gets appraisals. This must be true for self starters as well. A most critical point in projects where you actually want to ensure is that some how you should get a reference to evaluate. For example, if you develop a piece of software (for this purpose), it might be best to publish it to end user or open source it - so user critic and stats tells (anyone neutral) how big deal it is. If you do some other kind of project - seek who can be a potential user - may be donate your prototype to some academic lab or something for actual use and get recommendation in return. And if it is pure theoretical see if you can publish that somewhere. (like some magazine, blog etc.)
Peer reviewed work has always highest value in any science and engineering work..
In general, like any other projects during the job, additional project which is based on relevance to the position you are applying, but a listing of additional projects shows that you are self-driven enthusiast and that is always a great point.
See this: http://programmers.stackexchange.com/questions/134532/does-contributing-to-open-source-projects-to-boost-a-resume-make-sense/134538#134538