I run a blog for programming and development tutorials. I am planning to set up a subdomain and host my exercises there for the visitors so that, they can experience the tutorials/ code examples in a live demo. Now, I am wondering whether should I keep all pages on demo site 'noindex'? Or is it OK if I keep them indexed? Will it add any SEO value? Not to mention, those examples won't have much texts/contents, just examples.
The problem you face mostly is the fact that the demos could be considered thin content and ultimately effect your website rankings. You could use no-index on theses but even then some juice gets leaked even when you use no-follow and this problem still occurs if you was to host the content on a sub domain.
For ranking purposes this is what I propose:
For example if its a simple jQuery slider then why not just host contained with in the same tutorial. This ultimately lowers your bounce rate and gives your site a USP which should generator people linking too. From what your planning to do your one of thousands of sites already doing this.
Thing's You Cant Host on Same Page
If you want to host CMS based systems or thing's that can't be embedded into the page then by all means you should transfer this a sub-domain, or you should consider filling some unique demo content and actually host it on the same domain - Again this is another USP and makes you different.
Focus on Quality Rather than Quantity
The only reason I would assume that you will be doing lite demos is that you don't want to spend to much to much time on setting them up with content. I personally think as an SEO stand point this is bad and you should focus on Quality rather Quantity. As I've mentioned in previous sections of this answer there is no reason not to fill in unqine content into the demos and doing so gives your site an EDGE over many.
If you don't want to use Unique content within the demo content itself then a noindex will do the trick, for convince and security reasons you should use CMS on subdomains if you do not want to spend time making Unique content. On the sub domain you don't need to worry about no index since this won't effect your rankings, just use a noindex on the external link.