I bought a refurbished computer few months ago - two (somewhat older) Xeon processors, 48Gb RAM, and a 1T SSD (actually two 500G RAID config).  I just noticed when I had the BIOS setup open for an unrelated reason that Hyperthreading was disabled.  Is there a reason why that would have been the default setup for a machine with these specs?  I enabled it, but now I'm having second thoughts since someone obviously felt it should be disabled.  It seems that Cakewalk / SPLAT would make use of it, but I never feel like I'm maxing out the CPU anyway, so??

Could be that the previous owner was running it as a server and the server software ran better with HT disabled. Or was a gamer, or an Overclocker/Benchmarker trying to set world records with apps like 3DMark, Unigine, gaming benchmarks, etc. But more likely the 1st option (where the primarily-used software on the computer runs better with HT completely disabled in the BIOS). These days most modern software supports HT, but can still have problems with it.

Intel hyper-threading has been around since 2002.  I would leave it on.  It most likely will not hurt, but could give a slight performance boost.  I always disable CPU power management.  I like things locked to the full clock speed, but never mess with overclocking.
 
Hyper-threading gets mentioned in this SOS review of CPU performance, but no mention of disabling it.
https://www.soundonsound.com/reviews/cpu-performance-tested
 
 

When the first generation of Hyper-Threading was released, it caused a problem mainly with Cubase (IIRC).
Now ~16 years later, Hyper-Threading works completely smooth with all major DAW applications.
 
Note the CPU clock-speed on the XEON CPUs.
Often times, they're running at significantly slower clock-speed (which will affect DAW performance).