All cabins come with basic amenities, such as the services of a cabin steward to clean your room and turn down the beds, soap and shampoo in the bathroom, individual climate control, etc. But certain categories of stateroom come with added perks. Suites come with a variety of extras and privileges, everything from priority boarding to in-cabin bar setups. Spa cabins will offer spa-related perks, such as yoga mats in the cabin or a fancy showerhead; concierge-level cabins will give you access to a concierge and niceties like afternoon canapes; and even solo cabins might offer extras, such as the use of an exclusive lounge. How do you want to be pampered on your vacation?
In order to set the pricing many cruise lines will divide each cabin type into sub categories. For example a balcony cabin may be divided into sub categories such as B1, B2, B3, B4. In most cases the cabin size and features in a sub category is the exactly the same. The only difference is usually the location of the cabin on the ship. Please look for the notes on the category descriptions to determine if there is a difference in size or features between the subcategories.
Inside cabins with no views at all are typically the smallest, cheapest cabins onboard. They are great options for budget-minded travelers who do not intend to spend a lot of time in their stateroom, or who want to sleep all day in absolute pitch dark. They are less ideal for cruisers prone to seasickness, those who need natural light and groups who require a lot of in-cabin space. Not everyone will be happy in an inside cabin; it is worth upgrading if the lack of light will put a damper on your vacation.
Exception: Carnival has several cabins which are classified as inside cabins but actually have a french glass door which allows light into the room (no balcony, but the door can be opened). Carnival also has some cabins that have a window, but because the window has an obstructed view (that means there is a railing or object in the way) it is listed as an inside cabin. Royal Caribbean has some cabins that have a window but look out over an inside promenade area. These are called "promenade staterooms".