That depends on what kind of site you want and what you want your site to do for you. Generally speaking, you can host your site almost anywhere.
Though many clients like to consolidate services (domain/hosting/web designer in one), if you already have a site host, it's likely that you won't need to do a thing and you are not obligated to move to Monterey Bay Design. Most servers will offer all the support you'll need.
If you are "self-hosted," are on a basic personal webpage package with your ISP, or if your site does not support the platform or protocols necessary for a blog or other database-driven application to function, you may wish to host your site elsewhere. In this case, Monterey Bay Design would be happy to host you.