Sub-domain or sub-directory?
Installing your site niche (store, shop, wiki, etc) with a sub-domain or using it as your ongoing continuation - in a sub-directory? What sounds better for you?
shop.pennysite.com
pennysite.com/shop
In both cases, the physical location of your future website would still be in a sub-folder of your public.html directory, but the server and search engines would treat it differently. Servers will point to it as to a separate website, if you choose the sub-domain option. If you choose to install your extension in a sub-folder, search engines may assess it as a continuation of your website, or just as a sub-site. It is all for the search engines to decide.
What do you represent?
Do you want to represent a separate entity? Team? A sandbox platform? A brand? Or you are just trying to extend the existing flow?
There are many questions to answer:
- what is your niche?
- how big are you?
- what are your future prospects?
- what is you platform?
- how long is your domain name?
- is your main domain's CMS flexible enough to attain both goals, you are trying to set with sub-domains?
- do you have to install additional software, CMS?
There are tonnes of SEO experts, who insist on using the sub-directory installation over the sub-domain. They may be right, from the tech standpoint - but is your site trying to achieve only the SEO? Is your niche only traffic-oriented and does not fall into the: product, image, brand -awareness category?
Is your head site personal or business only?
If there is no personal connection between your mainsite.com and the new entity, you're trying to create, then installing your shop or blog into a sub-directory is a no-brainer. Sub-domains work well, if you want to substantiate two different flows. E.g., if your new entity is a completely different thing, or potentially conflicting (design-wise, brand-wise, tech-wise, etc) with you main site.
Stop thinking only about the SEO
The SEO algorithms change all the time, don't get beguiled here. If your entities are completely different, then try to use them in a sub-domain - as if they are different websites. Otherwise, you would:
- create a competition against yourself
- tarnish you main domain's brand image
- drive customers away
If your website is not personal, brand-oriented, or anyhow sensitive to public judgement; if its valued by ease of access, product range, services you offer, and if it serves a logical continuation of your head site - then installing into a sub-directory could be a big win for you. If it's technically possible on your server side (!!!)
Advantages of sub-directories:
- you'd accumulate more traffic
- you'd save on SSL
- you'd gain navigation speed
In this case, your sub-domain would be redundant. Why would I move into a different area, waste my time in navigating, adapting to a new design, etc, by visiting a separate site - if both of them are almost the same entity? Or serve the same purpose! In this case, users of your site would be only confused.
Conclusions
Does your new entity represent something completely different from the main domain? Could it damage your image (brand) anyhow, if you would stay in a sub-directory? Are you financially ready to truly branch-out? New SSL, emails, probably new hosting plan, a support team? Then go with the sub-domain!
Your new entity is just a logical and stylistic continuation of your main site? Your new entity is not much different from the main site? You would run them both on similar CMS frameworks? You would apply a very similar design? You're tech-oriented, rather than brand? Use the sub-directory!