There is a book out there in which a chap does a really good job of threading and chambering rifle barrels using one of the combination machines. He understands the machine and works with it.
I'm sure I would rather have one than nothing at all.
Older manual machines are not used a lot in industrial settings any more. Larger machines are intimidating to home users - moving the suckers can be interesting. My 16" SB had an 8' bed, cast iron pedestals, etc. It was heavy. Had to be moved down a flight of stairs. Even with professionals doing it, it was a bit scary. Not something to attempt with a couple of friends and a case of beer.
My SM is 7 ' long; the bucket of the loader that delivered it was 8", my shop door is 9'. Worked out just fine. Waltzed it around the concrete floor using pipe rollers. Remarkably easy.
Sometimes larger machines are less expensive than smaller ones, because moving them can be a challenge. Use professionals. They have the equipment and experience.
While I was still on the tools, Millwright, I moved a lot of lathes, milling machines and later CNC machines at the glass container factory I worked at.
It always amazed me how much such heavy frames could bend and come back to where they needed to be true, if they were set up properly.
I also had to move the huge glass blowing machines, which were every bit as sensetive and several times the mass in their cast steel frames. Again, they could and did come back to true when properly set up.
That doesn't mean a lathe or any other large machine base which has been cast from iron or steel can't be bent or set up so that it won't run true.
That's where professionals come in handy.
Many Machinists are easily capable of moving their machines and setting them up properly so don't take this as a diss. Sadly, many don't have a clue where to start and the same goes for laborers pressed into the project.
Be careful when moving and setting up your lathes is very good advice. Try to set them up on SOLID CONCRETE floors and on proper benches, preferrably made specifically for the particular lathe/milling machine if it's one of he larger units.
I've seen large lathes set up on heavy wooden decks in some sawmills but even when mounted on 12cm thick planks, you can feel the floor vibrate when the machines were started.
Level, across ends, centers, along the ways for the full length is imperative IMHO and that takes a very expensive and precice level to accomplish.
Small table top type lathes can be set up to be true with a bit of common sense and care. If your table isn't stable, your lathe won't be stable or run true.
My machines are both manual, I had the opportunity to take a similar sized early model CNC machine home with me when the plant closed but space was at a premium in my shop. I did manage to grab a bunch of tooling from it before it went to the scrap metal dealer. I would have taken the motor but it was 3 phase.
The lathe itself is expensive, good tooling, such as tool posts with removable tool holders or four sided Turret types aren't cheap. Then factor in the cost of decent sets of inside and outside micrometers up to 12cm. You can likely get by with smaller units but the complete sets are only a few dollars more expensive. Another good investment if you can afford it is a solid height micrometer and and depth micrometer. Then of course you need a run out dial indicator for setting up your bore for true in the chuck and in the spindle spider at the rear.
Don't foget proper cutting tool holders and the cutter heads that fit on them, and keep a supply of different size tool bits that can be ground for the shape of your threads. By the time all of this comes together, where you aren't mucking around for lack of proper tooling, the cost will come close to the price of the lathe.
Oh, lest I forget, it's always handy to have a faceplate with centre and a good dogleg for turning between centers to make cutting tapers on a barrel blank easier. Then of course steady rests, full and half.
If the lathe you're looking at doesn't come with a good supply of this equipment/tooling, you won't be able to get as much out of it as you should be able to
That doesn't mean you shouldn't purchase the lathe if it doesn't have all of these accessories. Just be aware of the added costs of purchasing reliably repeatable, quality tools needed to do a lot of the work you may need for the projects you intend to do.
Many factories and even some shops buy bare machines because they have lots of the accessories on hand or because the machine will be used for one or two specific types of jobs and just don't want the clutter of the accessories.
I saw a machine a few weeks ago, that only came with a six jaw chuck and a rocking type tool post. The owner didn't need or want anything else to gather dust and sold off all of the accessories.
Keep in mind, that there are a whole lot of 'right' ways to do any job in a machine shop, and that guys telling you what worked for them, are simply relating their experiences. Anything that results in a good part, within tolerances, is good! Well, Safe counts too! 
