Why would you want a table that incorporates some hidden seating? Well, for one thing, it certainly saves space. The stools that come with these types of tables fit under the tabletop so that when not in use, they take up no extra space at all. These seats being low, they can also be used as footstools. Another reason to opt for this type of table/chair combination is aesthetic: depending on the model, they can actually be quite attractive.
I find this model pretty cool:
Round table with hidden chairs pictured: Homelegance 3217PU* 5-Piece Gas Lift Dining Table Set, Dark Cherry Finish
This type of table can be ideal in a dorm room, which are often small. It is also ideal for a bar area, or anywhere parties are held.