Dado blades are a popular item in most woodworking shops, and give a table saw much more versatility.  They are available in the original steel tipped version or carbide tipped.  For those who won't be using the dado blade much, or who uses softer woods to make yard furniture, the steel tipped blade is adequate.   There are a few types of carbide dado blades.  The stacked type is sandwiched together, and then test cuts are made for width adjustments using metal or paper shims. Have plenty of scrap wood available for making test cuts.  The wobble dado is a blade mounted on a hub that allows it to be adjusted "tilted" which adjusts the cut.  The wobble blade is less expensive, but  is not always as flat as the stacking dado, or the new, permanent type.  It is also slightly more time consuming to get the adjustments correct.

Carbide tipped dado blades last a very long time.  Using a Dado blade often requires the use of a micrometer or precision calipers to get an accurate setting.   One popular European saw blade manufacturer now makes a Dado blade especially designed for cutting 1/4" and 3/8" channels, which is beneficial for box joints.  The reason for this is to eliminate measuring and shimming, and the blade is said to cut flat and clean box joints.  

Some smaller diameter carbide blades  (6" diameter) are less expensive, but don't cut as deep as the larger diameter blades.  A smaller  diameter dado set might be easier on a small table saw with less that 1 hp motor.  Also, some very inexpensive table saws do not have a large enough arbor to handle a dado blade.

It is recommended that you make, or purchase a few zero clearance inserts for your various width of dado blades. That is because there is the occasion when you will raise the blade very high and then have more space than required for most other dado cuts.  Also, the different widths of cuts require different inserts for the best results.  

Dado blades are great for making shelves, rabbit joints. and box joints.  Box joints are a great task to achieve with a table saw. They give you an added confidence and sense accomplishment.  Making box joints on a saw will help in gaining familiarity with gauges, measuring and doing more precision work with machines in general.  Many people who make dovetail joints don't consider the amount of experience gained from this alternate technique using a dado blade.  Making dovetails properly doesn't require much use or much  experience with a table saw.   Making box joints also helps you to learn about the different types of wood, the various blades, precision and mechanical efficiency, and a broad understanding and familiarity of a table saw in general.....work safe!

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