A domain must be unique (for example there can only be one single Yahoo.com) and must be registered with a domain registrar (ie. NameCheap); while for sub domains, users can freely add it on top of the existing domain as long as their web host provide the service. Some would say sub-domains are the ‘third level’ domains in the sense that they are simply “sub folders” under the domain root directory, normally used to organize your website content in different languages or different categories.
We regularly examine customer bandwidth and disk space utilization data in a series of statistical analyses and use the results to define "normal". Although these tests vary from month to month, one thing remains constant: 99.95% of our customers fall into "normal" range. If your account's bandwidth or disk space utilization causes any concern, you will receive an email asking you to reduce usage. We strive to provide at least 48 hours notice to allow customers to make adjustments before we take any corrective action.
Migration or transfer services are often free or offered at a reasonable fee. These services help move your existing site to the new hosting provider. They can save a huge amount of hassle. Just remember that the migration process is often automated, and may fit in with the host's processes and needs rather than yours. Not everything may migrate, and you may find the organization of the newly migrated site makes for harder maintenance in the long run.
In terms of what many vendors call unlimited service, Web Hosting Pad's terms of service indicate that their definition of unlimited is what they call "incremental." Basically, as you need more capability, they want to discuss that with you, both to help you get the most out of their services, and to make sure you're using their systems without abusing them.
Enterprise websites include very popular marketing and media sites, as well as social, travel, and other application-heavy websites. For example, Lamborghini, Coursera, and Nordstrom use AWS to host their websites. Enterprise websites need to dynamically scale resources and be highly available to support the most demanding and highly trafficked websites.
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.