Learning on worn out machines is sort of like practicing with a Benchrest Rifle that is locked into a .300 agg capability. It might go bang, but that is about it.
I disagree. There are literally thousands of tech school and high school shops that still use worn out and crashed South Bend Heavy 10's. There is not a lot to really wear out on them except the feed nuts, ways and spindle bearings.
SBL spindle bearings are sleeve bearings and are adjustable for free-play. A worn sleeve bearing will not "run out", it will just create some slop that may result in chatter in certain conditions of turning and boring with certain tooling but it will not create out-of-round diameters.
Worn ball or roller bearings can create out-of-round diameters if the balls, rollers, or races become chipped.
The bedway wear is only a factor if you are turning long diameters.
A worn tailstock, like Butch states, is not a factor in chamber reaming unless you try to use some of the so called "floating" reamer holders.
SBL Heavy 10's were made literally by the hundreds of thousands so used parts are available in many places. South Bend Lathe Co still offers new parts, even for the older models. I have a 1944 H-10 made for the US Navy and I got a cross feed nut for it from South Bend in 2 days.
It has been said many times, a good machinist can take a worn lathe and make good parts, but a bad machinist can not take a new lathe and make good parts.
How does one get to be a good machinist? Practice!! Practice on a good lathe like a SBL H-20 or Monarch EE or the like.
Much of this junk coming in now from Communist China is just that-junk. It will look good and has new paint, but run it for a while and it is junk. The type castings and bearings used on much of these imports are fine for the short term but go out and look in the machining industry and see how many of these imports they have.
In my 40+ year career as, among other things, as Manufacturing Engineer for a large chemical company (18,000+ employees) and as an educator and a technical adviser to three technical community colleges, and as a designer of US Department of Labor Bureau of Apprentice Training machinist certification programs I have visited many many school and industry shops. They have all used South Bend Lathes for some of the training.
I can give you a long list of benchrest gunsmiths that use SBL H-10's also.