If you buy a head, you'll have to get a cabinet with it. But the size and how many, depends on what you need.
Sure, you can connect 2 cabinets to an amp like that, but I doubt a lot of people actually really need it.
Another thing is, that you can use any size of cabinet you wish too. 1X12, 2X12, 4X12, it just depends on your needs.
A lot of guitar players always have stacks and stacks of cabinets on stage, yet, they only use 1 or 2 of them. They need it for looks, not for the sound. Cabinets get mic'ed up anyway, so the louder the volume would be on the stage coming from the amps, the more problems it would give for creating a decent mix both front of house, and monitors.
However, if you're like me, and play(or at least I used to) in a band that never scores gigs where they have a PA, you'll have to rely solely on your amp. In this case it is useful the have two 4X12 cabs stacked on eachother, just cause it spreads the sound a lot better. Personally I never used more than one, but it did the trick too.
For rehearsels, I always used one 2X12, elevated a little bit, pointed towards me. Workerd perfectly.
