You could think of the sites that share your server as your roommates; there's really not that much separating you from them. Sure, you can close the bedroom door, but they can still cause nightmares for you in the kitchen and the bathroom. In web hosting terms, all the sites share a single server's resources, so huge traffic spike on Site A may impact the neighboring sites' performances. It's even possible that another site could take down the shared server altogether, if it crashed hard enough.
If you've ever been worried about the tremendous amount of power large data centers consume, you might want to sign up with Green Geeks. The "green" in the company's name reflects the Green Geeks' commitment to the environment. It purchases three times the energy it actually uses in wind energy credits, essentially putting energy back into the economy. The company does this through a form of renewable energy certificates, which, while a bit complicated, means that it's not just energy neutral, i's actually helping fuel the green energy economy.
Almost all the services offer some sort of page builder that makes it easy to drag and drop to build your page. These are great for getting started, but they often lock you into the service. Most page builders are proprietary to the service, or don't create HTML that's portable enough to be easily moved to another service if you decide it's necessary.