Tube amplifiers mostly come in two different styles; head only, where speakers have to be connected separately, and combo amps, where the case is more of an all-in-one kind of thing, with amplifier and speakers all included in the same frame. Each type has its benefits for different kinds of guitar players, and it is important to think things through before making any kind of investment in a tube amplifier.
Starting with the kind which is by far more common and useful for the majority of players, the combo has a lot of benefits. For a start, the obvious thing is that the speakers and everything are all connected already, so this kind of amplifier is ready to make sound straight from the box. Another benefit is the fact that the speaker will be specifically chosen because it complements the amplifier it comes with. This means that the speaker is exactly right to work with the tube amp to produce exactly the right kind of tone and frequency range.
Another obvious plus is the fact that a combo is a little more convenient to transport and set up. You can carry one thing to a show, plug in and play, meaning that there is no need to hire a truck to take your amplifier and a number of different bulky speaker cabs with you each time. Convenience, economy and ease of use are some of the main reasons why such amplifier setups are common for practice amps, small gigs, intimate venue use and people learning to play the guitar.
The head setup is another matter entirely, and these kinds of tube amplifiers have no speaker in the case with them. Heads require a separate speaker cab to be attached to them to produce a sound, and so these types offer much more variety and customization of overall sound and tone. Individual speaker cabs can include reflex ports for stronger bass frequencies, angled speakers for wider sound coverage and even stereo configurations, all having different effects on the overall experience for the player and for the listener, and as there is no real limit to things like number of cabs and placement of speakers onstage, the amp head tends to be the choice for larger venues and players looking for specific tones and sound setups. Even though heads and cabs can be the more expensive route to go, the variety you can get from such a rig is well worth the money!