a Hobby site…

Summary:

In most cases it helps to at least start out with a non-commercial project. In short: hobby sites get more leeway.

Say you're in doubt about your next project. Should be a money maker or a hobby site? In that case choose the latter option for starters. There are a number of reasons for that, some a bit shadier than others, but all very valid. Of course — when you're up to it you can promote the site to a commercial status, by adding ads or an online shop.

Directories

Later on in this guide, you'll be advised to submit your site/pages to numerous directories. And since most webmasters starting out don't have money to burn, you're likely to prefer not paying for inclusion in these directories. As it happens there are lots of free directories about, but also lots that offer free inclusion for non-commercial sites only. Main example: the Zeal directory which doesn't even allow commercial sites for any sum of money. Funny though that most directories don't check if a site turns commercial overnight. (That said — Zeal has its own bot that visits included pages regularly…).

Frustration

Take the pressure off your site's performance — at least in the beginning. It's no use to put up a commercial site if no-one can find it. Work on popularity first. Of course: all this doesn't apply to outright shopping sites, but in general one can benefit from setting up a resource site first, and adding a shop later. Not only because of the objective reasons mentioned in this page's other paragraphs, but also because the lack of customers can move one to abandon the project prematurely.

Risk

Most webmasters actively involved in SEO just love to experiment. There are a lot of SEO methods to try out, and lots are quite successful. Keep in mind that some types of SEO are deemed "bad" by some of the search engines. Using these methods can lead to your site being penalised or even banned from the search results, which is of course not what you intended. However, it's quite safe to fool around with a hobby site, because a sudden drop in traffic won't hurt your wallet.

Fun

Have a site that suits your interests. Of course it could be worthwhile to have a well-running site selling bronze & silver funeral urns (for example — no offense intended), but you'll get bored long before you get there.